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Merge tag 'vfs-6.19-rc1.coredump' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs
Pull pidfd and coredump updates from Christian Brauner:
"Features:
- Expose coredump signal via pidfd
Expose the signal that caused the coredump through the pidfd
interface. The recent changes to rework coredump handling to rely
on unix sockets are in the process of being used in systemd. The
previous systemd coredump container interface requires the coredump
file descriptor and basic information including the signal number
to be sent to the container. This means the signal number needs to
be available before sending the coredump to the container.
- Add supported_mask field to pidfd
Add a new supported_mask field to struct pidfd_info that indicates
which information fields are supported by the running kernel. This
allows userspace to detect feature availability without relying on
error codes or kernel version checks.
Cleanups:
- Drop struct pidfs_exit_info and prepare to drop exit_info pointer,
simplifying the internal publication mechanism for exit and
coredump information retrievable via the pidfd ioctl
- Use guard() for task_lock in pidfs
- Reduce wait_pidfd lock scope
- Add missing PIDFD_INFO_SIZE_VER1 constant
- Add missing BUILD_BUG_ON() assert on struct pidfd_info
Fixes:
- Fix PIDFD_INFO_COREDUMP handling
Selftests:
- Split out coredump socket tests and common helpers into separate
files for better organization
- Fix userspace coredump client detection issues
- Handle edge-triggered epoll correctly
- Ignore ENOSPC errors in tests
- Add debug logging to coredump socket tests, socket protocol tests,
and test helpers
- Add tests for PIDFD_INFO_COREDUMP_SIGNAL
- Add tests for supported_mask field
- Update pidfd header for selftests"
* tag 'vfs-6.19-rc1.coredump' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (23 commits)
pidfs: reduce wait_pidfd lock scope
selftests/coredump: add second PIDFD_INFO_COREDUMP_SIGNAL test
selftests/coredump: add first PIDFD_INFO_COREDUMP_SIGNAL test
selftests/coredump: ignore ENOSPC errors
selftests/coredump: add debug logging to coredump socket protocol tests
selftests/coredump: add debug logging to coredump socket tests
selftests/coredump: add debug logging to test helpers
selftests/coredump: handle edge-triggered epoll correctly
selftests/coredump: fix userspace coredump client detection
selftests/coredump: fix userspace client detection
selftests/coredump: split out coredump socket tests
selftests/coredump: split out common helpers
selftests/pidfd: add second supported_mask test
selftests/pidfd: add first supported_mask test
selftests/pidfd: update pidfd header
pidfs: expose coredump signal
pidfs: drop struct pidfs_exit_info
pidfs: prepare to drop exit_info pointer
pidfd: add a new supported_mask field
pidfs: add missing BUILD_BUG_ON() assert on struct pidfd_info
...
While pidfs dentries are never hashed and thus retain_dentry() will never
consider them for placing them on the LRU it isn't great to always have
to go and remember that. Raise DCACHE_DONTCACHE explicitly as a visual
marker that dentries aren't kept but freed immediately instead.
Link: https://patch.msgid.link/20251029-work-namespace-nstree-listns-v4-4-2e6f823ebdc0@kernel.org
Tested-by: syzbot@syzkaller.appspotmail.com
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Userspace needs access to the signal that caused the coredump before the
coredumping process has been reaped. Expose it as part of the coredump
information in struct pidfd_info. After the process has been reaped that
info is also available as part of PIDFD_INFO_EXIT's exit_code field.
Link: https://patch.msgid.link/20251028-work-coredump-signal-v1-8-ca449b7b7aa0@kernel.org
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This is not needed anymore now that we have the new scheme to guarantee
all-or-nothing information exposure.
Link: https://patch.msgid.link/20251028-work-coredump-signal-v1-7-ca449b7b7aa0@kernel.org
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
There will likely be more info that we need to store in struct
pidfs_attr. We need to make sure that some of the information such as
exit info or coredump info that consists of multiple bits is either
available completely or not at all, but never partially. Currently we
use a pointer that we assign to. That doesn't scale. We can't waste a
pointer for each mulit-part information struct we want to expose. Use a
bitmask instead.
Link: https://patch.msgid.link/20251028-work-coredump-signal-v1-6-ca449b7b7aa0@kernel.org
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Some of the future fields in struct pidfd_info can be optional. If the
kernel has nothing to emit in that field, then it doesn't set the flag
in the reply. This presents a problem: There is currently no way to know
what mask flags the kernel supports since one can't always count on them
being in the reply.
Add a new PIDFD_INFO_SUPPORTED_MASK flag and field that the kernel can
set in the reply. Userspace can use this to determine if the fields it
requires from the kernel are supported. This also gives us a way to
deprecate fields in the future, if that should become necessary.
Link: https://patch.msgid.link/20251028-work-coredump-signal-v1-5-ca449b7b7aa0@kernel.org
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Validate that the size of struct pidfd_info is correctly updated.
Link: https://patch.msgid.link/20251028-work-coredump-signal-v1-4-ca449b7b7aa0@kernel.org
Fixes: 1d8db6fd69 ("pidfs, coredump: add PIDFD_INFO_COREDUMP")
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
When PIDFD_INFO_COREDUMP is requested we raise it unconditionally in the
returned mask even if no coredump actually did take place. This was
done because we assumed that the later check whether ->coredump_mask as
non-zero detects that it is zero and then retrieves the dumpability
settings from the task's mm. This has issues though becuase there are
tasks that might not have any mm. Also it's just not very cleanly
implemented. Fix this.
Link: https://patch.msgid.link/20251028-work-coredump-signal-v1-2-ca449b7b7aa0@kernel.org
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Merge tag 'pull-f_path' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull file->f_path constification from Al Viro:
"Only one thing was modifying ->f_path of an opened file - acct(2).
Massaging that away and constifying a bunch of struct path * arguments
in functions that might be given &file->f_path ends up with the
situation where we can turn ->f_path into an anon union of const
struct path f_path and struct path __f_path, the latter modified only
in a few places in fs/{file_table,open,namei}.c, all for struct file
instances that are yet to be opened"
* tag 'pull-f_path' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (23 commits)
Have cc(1) catch attempts to modify ->f_path
kernel/acct.c: saner struct file treatment
configfs:get_target() - release path as soon as we grab configfs_item reference
apparmor/af_unix: constify struct path * arguments
ovl_is_real_file: constify realpath argument
ovl_sync_file(): constify path argument
ovl_lower_dir(): constify path argument
ovl_get_verity_digest(): constify path argument
ovl_validate_verity(): constify {meta,data}path arguments
ovl_ensure_verity_loaded(): constify datapath argument
ksmbd_vfs_set_init_posix_acl(): constify path argument
ksmbd_vfs_inherit_posix_acl(): constify path argument
ksmbd_vfs_kern_path_unlock(): constify path argument
ksmbd_vfs_path_lookup_locked(): root_share_path can be const struct path *
check_export(): constify path argument
export_operations->open(): constify path argument
rqst_exp_get_by_name(): constify path argument
nfs: constify path argument of __vfs_getattr()
bpf...d_path(): constify path argument
done_path_create(): constify path argument
...
- The 3 patch series "mm, swap: improve cluster scan strategy" from
Kairui Song improves performance and reduces the failure rate of swap
cluster allocation.
- The 4 patch series "support large align and nid in Rust allocators"
from Vitaly Wool permits Rust allocators to set NUMA node and large
alignment when perforning slub and vmalloc reallocs.
- The 2 patch series "mm/damon/vaddr: support stat-purpose DAMOS" from
Yueyang Pan extend DAMOS_STAT's handling of the DAMON operations sets
for virtual address spaces for ops-level DAMOS filters.
- The 3 patch series "execute PROCMAP_QUERY ioctl under per-vma lock"
from Suren Baghdasaryan reduces mmap_lock contention during reads of
/proc/pid/maps.
- The 2 patch series "mm/mincore: minor clean up for swap cache
checking" from Kairui Song performs some cleanup in the swap code.
- The 11 patch series "mm: vm_normal_page*() improvements" from David
Hildenbrand provides code cleanup in the pagemap code.
- The 5 patch series "add persistent huge zero folio support" from
Pankaj Raghav provides a block layer speedup by optionalls making the
huge_zero_pagepersistent, instead of releasing it when its refcount
falls to zero.
- The 3 patch series "kho: fixes and cleanups" from Mike Rapoport adds a
few touchups to the recently added Kexec Handover feature.
- The 10 patch series "mm: make mm->flags a bitmap and 64-bit on all
arches" from Lorenzo Stoakes turns mm_struct.flags into a bitmap. To
end the constant struggle with space shortage on 32-bit conflicting with
64-bit's needs.
- The 2 patch series "mm/swapfile.c and swap.h cleanup" from Chris Li
cleans up some swap code.
- The 7 patch series "selftests/mm: Fix false positives and skip
unsupported tests" from Donet Tom fixes a few things in our selftests
code.
- The 7 patch series "prctl: extend PR_SET_THP_DISABLE to only provide
THPs when advised" from David Hildenbrand "allows individual processes
to opt-out of THP=always into THP=madvise, without affecting other
workloads on the system".
It's a long story - the [1/N] changelog spells out the considerations.
- The 11 patch series "Add and use memdesc_flags_t" from Matthew Wilcox
gets us started on the memdesc project. Please see
https://kernelnewbies.org/MatthewWilcox/Memdescs and
https://blogs.oracle.com/linux/post/introducing-memdesc.
- The 3 patch series "Tiny optimization for large read operations" from
Chi Zhiling improves the efficiency of the pagecache read path.
- The 5 patch series "Better split_huge_page_test result check" from Zi
Yan improves our folio splitting selftest code.
- The 2 patch series "test that rmap behaves as expected" from Wei Yang
adds some rmap selftests.
- The 3 patch series "remove write_cache_pages()" from Christoph Hellwig
removes that function and converts its two remaining callers.
- The 2 patch series "selftests/mm: uffd-stress fixes" from Dev Jain
fixes some UFFD selftests issues.
- The 3 patch series "introduce kernel file mapped folios" from Boris
Burkov introduces the concept of "kernel file pages". Using these
permits btrfs to account its metadata pages to the root cgroup, rather
than to the cgroups of random inappropriate tasks.
- The 2 patch series "mm/pageblock: improve readability of some
pageblock handling" from Wei Yang provides some readability improvements
to the page allocator code.
- The 11 patch series "mm/damon: support ARM32 with LPAE" from SeongJae
Park teaches DAMON to understand arm32 highmem.
- The 4 patch series "tools: testing: Use existing atomic.h for
vma/maple tests" from Brendan Jackman performs some code cleanups and
deduplication under tools/testing/.
- The 2 patch series "maple_tree: Fix testing for 32bit compiles" from
Liam Howlett fixes a couple of 32-bit issues in
tools/testing/radix-tree.c.
- The 2 patch series "kasan: unify kasan_enabled() and remove
arch-specific implementations" from Sabyrzhan Tasbolatov moves KASAN
arch-specific initialization code into a common arch-neutral
implementation.
- The 3 patch series "mm: remove zpool" from Johannes Weiner removes
zspool - an indirection layer which now only redirects to a single thing
(zsmalloc).
- The 2 patch series "mm: task_stack: Stack handling cleanups" from
Pasha Tatashin makes a couple of cleanups in the fork code.
- The 37 patch series "mm: remove nth_page()" from David Hildenbrand
makes rather a lot of adjustments at various nth_page() callsites,
eventually permitting the removal of that undesirable helper function.
- The 2 patch series "introduce kasan.write_only option in hw-tags" from
Yeoreum Yun creates a KASAN read-only mode for ARM, using that
architecture's memory tagging feature. It is felt that a read-only mode
KASAN is suitable for use in production systems rather than debug-only.
- The 3 patch series "mm: hugetlb: cleanup hugetlb folio allocation"
from Kefeng Wang does some tidying in the hugetlb folio allocation code.
- The 12 patch series "mm: establish const-correctness for pointer
parameters" from Max Kellermann makes quite a number of the MM API
functions more accurate about the constness of their arguments. This
was getting in the way of subsystems (in this case CEPH) when they
attempt to improving their own const/non-const accuracy.
- The 7 patch series "Cleanup free_pages() misuse" from Vishal Moola
fixes a number of code sites which were confused over when to use
free_pages() vs __free_pages().
- The 3 patch series "Add Rust abstraction for Maple Trees" from Alice
Ryhl makes the mapletree code accessible to Rust. Required by nouveau
and by its forthcoming successor: the new Rust Nova driver.
- The 2 patch series "selftests/mm: split_huge_page_test:
split_pte_mapped_thp improvements" from David Hildenbrand adds a fix and
some cleanups to the thp selftesting code.
- The 14 patch series "mm, swap: introduce swap table as swap cache
(phase I)" from Chris Li and Kairui Song is the first step along the
path to implementing "swap tables" - a new approach to swap allocation
and state tracking which is expected to yield speed and space
improvements. This patchset itself yields a 5-20% performance benefit
in some situations.
- The 3 patch series "Some ptdesc cleanups" from Matthew Wilcox utilizes
the new memdesc layer to clean up the ptdesc code a little.
- The 3 patch series "Fix va_high_addr_switch.sh test failure" from
Chunyu Hu fixes some issues in our 5-level pagetable selftesting code.
- The 2 patch series "Minor fixes for memory allocation profiling" from
Suren Baghdasaryan addresses a couple of minor issues in relatively new
memory allocation profiling feature.
- The 3 patch series "Small cleanups" from Matthew Wilcox has a few
cleanups in preparation for more memdesc work.
- The 2 patch series "mm/damon: add addr_unit for DAMON_LRU_SORT and
DAMON_RECLAIM" from Quanmin Yan makes some changes to DAMON in
furtherance of supporting arm highmem.
- The 2 patch series "selftests/mm: Add -Wunreachable-code and fix
warnings" from Muhammad Anjum adds that compiler check to selftests code
and fixes the fallout, by removing dead code.
- The 10 patch series "Improvements to Victim Process Thawing and OOM
Reaper Traversal Order" from zhongjinji makes a number of improvements
in the OOM killer: mainly thawing a more appropriate group of victim
threads so they can release resources.
- The 5 patch series "mm/damon: misc fixups and improvements for 6.18"
from SeongJae Park is a bunch of small and unrelated fixups for DAMON.
- The 7 patch series "mm/damon: define and use DAMON initialization
check function" from SeongJae Park implement reliability and
maintainability improvements to a recently-added bug fix.
- The 2 patch series "mm/damon/stat: expose auto-tuned intervals and
non-idle ages" from SeongJae Park provides additional transparency to
userspace clients of the DAMON_STAT information.
- The 2 patch series "Expand scope of khugepaged anonymous collapse"
from Dev Jain removes some constraints on khubepaged's collapsing of
anon VMAs. It also increases the success rate of MADV_COLLAPSE against
an anon vma.
- The 2 patch series "mm: do not assume file == vma->vm_file in
compat_vma_mmap_prepare()" from Lorenzo Stoakes moves us further towards
removal of file_operations.mmap(). This patchset concentrates upon
clearing up the treatment of stacked filesystems.
- The 6 patch series "mm: Improve mlock tracking for large folios" from
Kiryl Shutsemau provides some fixes and improvements to mlock's tracking
of large folios. /proc/meminfo's "Mlocked" field became more accurate.
- The 2 patch series "mm/ksm: Fix incorrect accounting of KSM counters
during fork" from Donet Tom fixes several user-visible KSM stats
inaccuracies across forks and adds selftest code to verify these
counters.
- The 2 patch series "mm_slot: fix the usage of mm_slot_entry" from Wei
Yang addresses some potential but presently benign issues in KSM's
mm_slot handling.
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Merge tag 'mm-stable-2025-10-01-19-00' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Pull MM updates from Andrew Morton:
- "mm, swap: improve cluster scan strategy" from Kairui Song improves
performance and reduces the failure rate of swap cluster allocation
- "support large align and nid in Rust allocators" from Vitaly Wool
permits Rust allocators to set NUMA node and large alignment when
perforning slub and vmalloc reallocs
- "mm/damon/vaddr: support stat-purpose DAMOS" from Yueyang Pan extend
DAMOS_STAT's handling of the DAMON operations sets for virtual
address spaces for ops-level DAMOS filters
- "execute PROCMAP_QUERY ioctl under per-vma lock" from Suren
Baghdasaryan reduces mmap_lock contention during reads of
/proc/pid/maps
- "mm/mincore: minor clean up for swap cache checking" from Kairui Song
performs some cleanup in the swap code
- "mm: vm_normal_page*() improvements" from David Hildenbrand provides
code cleanup in the pagemap code
- "add persistent huge zero folio support" from Pankaj Raghav provides
a block layer speedup by optionalls making the
huge_zero_pagepersistent, instead of releasing it when its refcount
falls to zero
- "kho: fixes and cleanups" from Mike Rapoport adds a few touchups to
the recently added Kexec Handover feature
- "mm: make mm->flags a bitmap and 64-bit on all arches" from Lorenzo
Stoakes turns mm_struct.flags into a bitmap. To end the constant
struggle with space shortage on 32-bit conflicting with 64-bit's
needs
- "mm/swapfile.c and swap.h cleanup" from Chris Li cleans up some swap
code
- "selftests/mm: Fix false positives and skip unsupported tests" from
Donet Tom fixes a few things in our selftests code
- "prctl: extend PR_SET_THP_DISABLE to only provide THPs when advised"
from David Hildenbrand "allows individual processes to opt-out of
THP=always into THP=madvise, without affecting other workloads on the
system".
It's a long story - the [1/N] changelog spells out the considerations
- "Add and use memdesc_flags_t" from Matthew Wilcox gets us started on
the memdesc project. Please see
https://kernelnewbies.org/MatthewWilcox/Memdescs and
https://blogs.oracle.com/linux/post/introducing-memdesc
- "Tiny optimization for large read operations" from Chi Zhiling
improves the efficiency of the pagecache read path
- "Better split_huge_page_test result check" from Zi Yan improves our
folio splitting selftest code
- "test that rmap behaves as expected" from Wei Yang adds some rmap
selftests
- "remove write_cache_pages()" from Christoph Hellwig removes that
function and converts its two remaining callers
- "selftests/mm: uffd-stress fixes" from Dev Jain fixes some UFFD
selftests issues
- "introduce kernel file mapped folios" from Boris Burkov introduces
the concept of "kernel file pages". Using these permits btrfs to
account its metadata pages to the root cgroup, rather than to the
cgroups of random inappropriate tasks
- "mm/pageblock: improve readability of some pageblock handling" from
Wei Yang provides some readability improvements to the page allocator
code
- "mm/damon: support ARM32 with LPAE" from SeongJae Park teaches DAMON
to understand arm32 highmem
- "tools: testing: Use existing atomic.h for vma/maple tests" from
Brendan Jackman performs some code cleanups and deduplication under
tools/testing/
- "maple_tree: Fix testing for 32bit compiles" from Liam Howlett fixes
a couple of 32-bit issues in tools/testing/radix-tree.c
- "kasan: unify kasan_enabled() and remove arch-specific
implementations" from Sabyrzhan Tasbolatov moves KASAN arch-specific
initialization code into a common arch-neutral implementation
- "mm: remove zpool" from Johannes Weiner removes zspool - an
indirection layer which now only redirects to a single thing
(zsmalloc)
- "mm: task_stack: Stack handling cleanups" from Pasha Tatashin makes a
couple of cleanups in the fork code
- "mm: remove nth_page()" from David Hildenbrand makes rather a lot of
adjustments at various nth_page() callsites, eventually permitting
the removal of that undesirable helper function
- "introduce kasan.write_only option in hw-tags" from Yeoreum Yun
creates a KASAN read-only mode for ARM, using that architecture's
memory tagging feature. It is felt that a read-only mode KASAN is
suitable for use in production systems rather than debug-only
- "mm: hugetlb: cleanup hugetlb folio allocation" from Kefeng Wang does
some tidying in the hugetlb folio allocation code
- "mm: establish const-correctness for pointer parameters" from Max
Kellermann makes quite a number of the MM API functions more accurate
about the constness of their arguments. This was getting in the way
of subsystems (in this case CEPH) when they attempt to improving
their own const/non-const accuracy
- "Cleanup free_pages() misuse" from Vishal Moola fixes a number of
code sites which were confused over when to use free_pages() vs
__free_pages()
- "Add Rust abstraction for Maple Trees" from Alice Ryhl makes the
mapletree code accessible to Rust. Required by nouveau and by its
forthcoming successor: the new Rust Nova driver
- "selftests/mm: split_huge_page_test: split_pte_mapped_thp
improvements" from David Hildenbrand adds a fix and some cleanups to
the thp selftesting code
- "mm, swap: introduce swap table as swap cache (phase I)" from Chris
Li and Kairui Song is the first step along the path to implementing
"swap tables" - a new approach to swap allocation and state tracking
which is expected to yield speed and space improvements. This
patchset itself yields a 5-20% performance benefit in some situations
- "Some ptdesc cleanups" from Matthew Wilcox utilizes the new memdesc
layer to clean up the ptdesc code a little
- "Fix va_high_addr_switch.sh test failure" from Chunyu Hu fixes some
issues in our 5-level pagetable selftesting code
- "Minor fixes for memory allocation profiling" from Suren Baghdasaryan
addresses a couple of minor issues in relatively new memory
allocation profiling feature
- "Small cleanups" from Matthew Wilcox has a few cleanups in
preparation for more memdesc work
- "mm/damon: add addr_unit for DAMON_LRU_SORT and DAMON_RECLAIM" from
Quanmin Yan makes some changes to DAMON in furtherance of supporting
arm highmem
- "selftests/mm: Add -Wunreachable-code and fix warnings" from Muhammad
Anjum adds that compiler check to selftests code and fixes the
fallout, by removing dead code
- "Improvements to Victim Process Thawing and OOM Reaper Traversal
Order" from zhongjinji makes a number of improvements in the OOM
killer: mainly thawing a more appropriate group of victim threads so
they can release resources
- "mm/damon: misc fixups and improvements for 6.18" from SeongJae Park
is a bunch of small and unrelated fixups for DAMON
- "mm/damon: define and use DAMON initialization check function" from
SeongJae Park implement reliability and maintainability improvements
to a recently-added bug fix
- "mm/damon/stat: expose auto-tuned intervals and non-idle ages" from
SeongJae Park provides additional transparency to userspace clients
of the DAMON_STAT information
- "Expand scope of khugepaged anonymous collapse" from Dev Jain removes
some constraints on khubepaged's collapsing of anon VMAs. It also
increases the success rate of MADV_COLLAPSE against an anon vma
- "mm: do not assume file == vma->vm_file in compat_vma_mmap_prepare()"
from Lorenzo Stoakes moves us further towards removal of
file_operations.mmap(). This patchset concentrates upon clearing up
the treatment of stacked filesystems
- "mm: Improve mlock tracking for large folios" from Kiryl Shutsemau
provides some fixes and improvements to mlock's tracking of large
folios. /proc/meminfo's "Mlocked" field became more accurate
- "mm/ksm: Fix incorrect accounting of KSM counters during fork" from
Donet Tom fixes several user-visible KSM stats inaccuracies across
forks and adds selftest code to verify these counters
- "mm_slot: fix the usage of mm_slot_entry" from Wei Yang addresses
some potential but presently benign issues in KSM's mm_slot handling
* tag 'mm-stable-2025-10-01-19-00' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (372 commits)
mm: swap: check for stable address space before operating on the VMA
mm: convert folio_page() back to a macro
mm/khugepaged: use start_addr/addr for improved readability
hugetlbfs: skip VMAs without shareable locks in hugetlb_vmdelete_list
alloc_tag: fix boot failure due to NULL pointer dereference
mm: silence data-race in update_hiwater_rss
mm/memory-failure: don't select MEMORY_ISOLATION
mm/khugepaged: remove definition of struct khugepaged_mm_slot
mm/ksm: get mm_slot by mm_slot_entry() when slot is !NULL
hugetlb: increase number of reserving hugepages via cmdline
selftests/mm: add fork inheritance test for ksm_merging_pages counter
mm/ksm: fix incorrect KSM counter handling in mm_struct during fork
drivers/base/node: fix double free in register_one_node()
mm: remove PMD alignment constraint in execmem_vmalloc()
mm/memory_hotplug: fix typo 'esecially' -> 'especially'
mm/rmap: improve mlock tracking for large folios
mm/filemap: map entire large folio faultaround
mm/fault: try to map the entire file folio in finish_fault()
mm/rmap: mlock large folios in try_to_unmap_one()
mm/rmap: fix a mlock race condition in folio_referenced_one()
...
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Merge tag 'namespace-6.18-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs
Pull namespace updates from Christian Brauner:
"This contains a larger set of changes around the generic namespace
infrastructure of the kernel.
Each specific namespace type (net, cgroup, mnt, ...) embedds a struct
ns_common which carries the reference count of the namespace and so
on.
We open-coded and cargo-culted so many quirks for each namespace type
that it just wasn't scalable anymore. So given there's a bunch of new
changes coming in that area I've started cleaning all of this up.
The core change is to make it possible to correctly initialize every
namespace uniformly and derive the correct initialization settings
from the type of the namespace such as namespace operations, namespace
type and so on. This leaves the new ns_common_init() function with a
single parameter which is the specific namespace type which derives
the correct parameters statically. This also means the compiler will
yell as soon as someone does something remotely fishy.
The ns_common_init() addition also allows us to remove ns_alloc_inum()
and drops any special-casing of the initial network namespace in the
network namespace initialization code that Linus complained about.
Another part is reworking the reference counting. The reference
counting was open-coded and copy-pasted for each namespace type even
though they all followed the same rules. This also removes all open
accesses to the reference count and makes it private and only uses a
very small set of dedicated helpers to manipulate them just like we do
for e.g., files.
In addition this generalizes the mount namespace iteration
infrastructure introduced a few cycles ago. As reminder, the vfs makes
it possible to iterate sequentially and bidirectionally through all
mount namespaces on the system or all mount namespaces that the caller
holds privilege over. This allow userspace to iterate over all mounts
in all mount namespaces using the listmount() and statmount() system
call.
Each mount namespace has a unique identifier for the lifetime of the
systems that is exposed to userspace. The network namespace also has a
unique identifier working exactly the same way. This extends the
concept to all other namespace types.
The new nstree type makes it possible to lookup namespaces purely by
their identifier and to walk the namespace list sequentially and
bidirectionally for all namespace types, allowing userspace to iterate
through all namespaces. Looking up namespaces in the namespace tree
works completely locklessly.
This also means we can move the mount namespace onto the generic
infrastructure and remove a bunch of code and members from struct
mnt_namespace itself.
There's a bunch of stuff coming on top of this in the future but for
now this uses the generic namespace tree to extend a concept
introduced first for pidfs a few cycles ago. For a while now we have
supported pidfs file handles for pidfds. This has proven to be very
useful.
This extends the concept to cover namespaces as well. It is possible
to encode and decode namespace file handles using the common
name_to_handle_at() and open_by_handle_at() apis.
As with pidfs file handles, namespace file handles are exhaustive,
meaning it is not required to actually hold a reference to nsfs in
able to decode aka open_by_handle_at() a namespace file handle.
Instead the FD_NSFS_ROOT constant can be passed which will let the
kernel grab a reference to the root of nsfs internally and thus decode
the file handle.
Namespaces file descriptors can already be derived from pidfds which
means they aren't subject to overmount protection bugs. IOW, it's
irrelevant if the caller would not have access to an appropriate
/proc/<pid>/ns/ directory as they could always just derive the
namespace based on a pidfd already.
It has the same advantage as pidfds. It's possible to reliably and for
the lifetime of the system refer to a namespace without pinning any
resources and to compare them trivially.
Permission checking is kept simple. If the caller is located in the
namespace the file handle refers to they are able to open it otherwise
they must hold privilege over the owning namespace of the relevant
namespace.
The namespace file handle layout is exposed as uapi and has a stable
and extensible format. For now it simply contains the namespace
identifier, the namespace type, and the inode number. The stable
format means that userspace may construct its own namespace file
handles without going through name_to_handle_at() as they are already
allowed for pidfs and cgroup file handles"
* tag 'namespace-6.18-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (65 commits)
ns: drop assert
ns: move ns type into struct ns_common
nstree: make struct ns_tree private
ns: add ns_debug()
ns: simplify ns_common_init() further
cgroup: add missing ns_common include
ns: use inode initializer for initial namespaces
selftests/namespaces: verify initial namespace inode numbers
ns: rename to __ns_ref
nsfs: port to ns_ref_*() helpers
net: port to ns_ref_*() helpers
uts: port to ns_ref_*() helpers
ipv4: use check_net()
net: use check_net()
net-sysfs: use check_net()
user: port to ns_ref_*() helpers
time: port to ns_ref_*() helpers
pid: port to ns_ref_*() helpers
ipc: port to ns_ref_*() helpers
cgroup: port to ns_ref_*() helpers
...
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Merge tag 'vfs-6.18-rc1.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs
Pull misc vfs updates from Christian Brauner:
"This contains the usual selections of misc updates for this cycle.
Features:
- Add "initramfs_options" parameter to set initramfs mount options.
This allows to add specific mount options to the rootfs to e.g.,
limit the memory size
- Add RWF_NOSIGNAL flag for pwritev2()
Add RWF_NOSIGNAL flag for pwritev2. This flag prevents the SIGPIPE
signal from being raised when writing on disconnected pipes or
sockets. The flag is handled directly by the pipe filesystem and
converted to the existing MSG_NOSIGNAL flag for sockets
- Allow to pass pid namespace as procfs mount option
Ever since the introduction of pid namespaces, procfs has had very
implicit behaviour surrounding them (the pidns used by a procfs
mount is auto-selected based on the mounting process's active
pidns, and the pidns itself is basically hidden once the mount has
been constructed)
This implicit behaviour has historically meant that userspace was
required to do some special dances in order to configure the pidns
of a procfs mount as desired. Examples include:
* In order to bypass the mnt_too_revealing() check, Kubernetes
creates a procfs mount from an empty pidns so that user
namespaced containers can be nested (without this, the nested
containers would fail to mount procfs)
But this requires forking off a helper process because you cannot
just one-shot this using mount(2)
* Container runtimes in general need to fork into a container
before configuring its mounts, which can lead to security issues
in the case of shared-pidns containers (a privileged process in
the pidns can interact with your container runtime process)
While SUID_DUMP_DISABLE and user namespaces make this less of an
issue, the strict need for this due to a minor uAPI wart is kind
of unfortunate
Things would be much easier if there was a way for userspace to
just specify the pidns they want. So this pull request contains
changes to implement a new "pidns" argument which can be set
using fsconfig(2):
fsconfig(procfd, FSCONFIG_SET_FD, "pidns", NULL, nsfd);
fsconfig(procfd, FSCONFIG_SET_STRING, "pidns", "/proc/self/ns/pid", 0);
or classic mount(2) / mount(8):
// mount -t proc -o pidns=/proc/self/ns/pid proc /tmp/proc
mount("proc", "/tmp/proc", "proc", MS_..., "pidns=/proc/self/ns/pid");
Cleanups:
- Remove the last references to EXPORT_OP_ASYNC_LOCK
- Make file_remove_privs_flags() static
- Remove redundant __GFP_NOWARN when GFP_NOWAIT is used
- Use try_cmpxchg() in start_dir_add()
- Use try_cmpxchg() in sb_init_done_wq()
- Replace offsetof() with struct_size() in ioctl_file_dedupe_range()
- Remove vfs_ioctl() export
- Replace rwlock() with spinlock in epoll code as rwlock causes
priority inversion on preempt rt kernels
- Make ns_entries in fs/proc/namespaces const
- Use a switch() statement() in init_special_inode() just like we do
in may_open()
- Use struct_size() in dir_add() in the initramfs code
- Use str_plural() in rd_load_image()
- Replace strcpy() with strscpy() in find_link()
- Rename generic_delete_inode() to inode_just_drop() and
generic_drop_inode() to inode_generic_drop()
- Remove unused arguments from fcntl_{g,s}et_rw_hint()
Fixes:
- Document @name parameter for name_contains_dotdot() helper
- Fix spelling mistake
- Always return zero from replace_fd() instead of the file descriptor
number
- Limit the size for copy_file_range() in compat mode to prevent a
signed overflow
- Fix debugfs mount options not being applied
- Verify the inode mode when loading it from disk in minixfs
- Verify the inode mode when loading it from disk in cramfs
- Don't trigger automounts with RESOLVE_NO_XDEV
If openat2() was called with RESOLVE_NO_XDEV it didn't traverse
through automounts, but could still trigger them
- Add FL_RECLAIM flag to show_fl_flags() macro so it appears in
tracepoints
- Fix unused variable warning in rd_load_image() on s390
- Make INITRAMFS_PRESERVE_MTIME depend on BLK_DEV_INITRD
- Use ns_capable_noaudit() when determining net sysctl permissions
- Don't call path_put() under namespace semaphore in listmount() and
statmount()"
* tag 'vfs-6.18-rc1.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (38 commits)
fcntl: trim arguments
listmount: don't call path_put() under namespace semaphore
statmount: don't call path_put() under namespace semaphore
pid: use ns_capable_noaudit() when determining net sysctl permissions
fs: rename generic_delete_inode() and generic_drop_inode()
init: INITRAMFS_PRESERVE_MTIME should depend on BLK_DEV_INITRD
initramfs: Replace strcpy() with strscpy() in find_link()
initrd: Use str_plural() in rd_load_image()
initramfs: Use struct_size() helper to improve dir_add()
initrd: Fix unused variable warning in rd_load_image() on s390
fs: use the switch statement in init_special_inode()
fs/proc/namespaces: make ns_entries const
filelock: add FL_RECLAIM to show_fl_flags() macro
eventpoll: Replace rwlock with spinlock
selftests/proc: add tests for new pidns APIs
procfs: add "pidns" mount option
pidns: move is-ancestor logic to helper
openat2: don't trigger automounts with RESOLVE_NO_XDEV
namei: move cross-device check to __traverse_mounts
namei: remove LOOKUP_NO_XDEV check from handle_mounts
...
for the method and its sole instance...
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
generic_delete_inode() is rather misleading for what the routine is
doing. inode_just_drop() should be much clearer.
The new naming is inconsistent with generic_drop_inode(), so rename that
one as well with inode_ as the suffix.
No functional changes.
Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Validate extensible ioctls stricter than we do now.
Reviewed-by: Aleksa Sarai <cyphar@cyphar.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
The coredump logic is slightly different from other users in that it both
stores mm flags and additionally sets and gets using masks.
Since the MMF_DUMPABLE_* flags must remain as they are for uABI reasons,
and of course these are within the first 32-bits of the flags, it is
reasonable to provide access to these in the same fashion so this logic
can all still keep working as it has been.
Therefore, introduce coredump-specific helpers __mm_flags_get_dumpable()
and __mm_flags_set_mask_dumpable() for this purpose, and update all core
dump users of mm flags to use these.
[lorenzo.stoakes@oracle.com: abstract set_mask_bits() invocation to mm_types.h to satisfy ARC]
Link: https://lkml.kernel.org/r/0e7ad263-1ff7-446d-81fe-97cff9c0e7ed@lucifer.local
Link: https://lkml.kernel.org/r/2a5075f7e3c5b367d988178c79a3063d12ee53a9.1755012943.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Borislav Betkov <bp@alien8.de>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: David Rientjes <rientjes@google.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Marc Rutland <mark.rutland@arm.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mel Gorman <mgorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Namhyung kim <namhyung@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: xu xin <xu.xin16@zte.com.cn>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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Merge tag 'vfs-6.17-rc1.pidfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs
Pull pidfs updates from Christian Brauner:
- persistent info
Persist exit and coredump information independent of whether anyone
currently holds a pidfd for the struct pid.
The current scheme allocated pidfs dentries on-demand repeatedly.
This scheme is reaching it's limits as it makes it impossible to pin
information that needs to be available after the task has exited or
coredumped and that should not be lost simply because the pidfd got
closed temporarily. The next opener should still see the stashed
information.
This is also a prerequisite for supporting extended attributes on
pidfds to allow attaching meta information to them.
If someone opens a pidfd for a struct pid a pidfs dentry is allocated
and stashed in pid->stashed. Once the last pidfd for the struct pid
is closed the pidfs dentry is released and removed from pid->stashed.
So if 10 callers create a pidfs dentry for the same struct pid
sequentially, i.e., each closing the pidfd before the other creates a
new one then a new pidfs dentry is allocated every time.
Because multiple tasks acquiring and releasing a pidfd for the same
struct pid can race with each another a task may still find a valid
pidfs entry from the previous task in pid->stashed and reuse it. Or
it might find a dead dentry in there and fail to reuse it and so
stashes a new pidfs dentry. Multiple tasks may race to stash a new
pidfs dentry but only one will succeed, the other ones will put their
dentry.
The current scheme aims to ensure that a pidfs dentry for a struct
pid can only be created if the task is still alive or if a pidfs
dentry already existed before the task was reaped and so exit
information has been was stashed in the pidfs inode.
That's great except that it's buggy. If a pidfs dentry is stashed in
pid->stashed after pidfs_exit() but before __unhash_process() is
called we will return a pidfd for a reaped task without exit
information being available.
The pidfds_pid_valid() check does not guard against this race as it
doens't sync at all with pidfs_exit(). The pid_has_task() check might
be successful simply because we're before __unhash_process() but
after pidfs_exit().
Introduce a new scheme where the lifetime of information associated
with a pidfs entry (coredump and exit information) isn't bound to the
lifetime of the pidfs inode but the struct pid itself.
The first time a pidfs dentry is allocated for a struct pid a struct
pidfs_attr will be allocated which will be used to store exit and
coredump information.
If all pidfs for the pidfs dentry are closed the dentry and inode can
be cleaned up but the struct pidfs_attr will stick until the struct
pid itself is freed. This will ensure minimal memory usage while
persisting relevant information.
The new scheme has various advantages. First, it allows to close the
race where we end up handing out a pidfd for a reaped task for which
no exit information is available. Second, it minimizes memory usage.
Third, it allows to remove complex lifetime tracking via dentries
when registering a struct pid with pidfs. There's no need to get or
put a reference. Instead, the lifetime of exit and coredump
information associated with a struct pid is bound to the lifetime of
struct pid itself.
- extended attributes
Now that we have a way to persist information for pidfs dentries we
can start supporting extended attributes on pidfds. This will allow
userspace to attach meta information to tasks.
One natural extension would be to introduce a custom pidfs.* extended
attribute space and allow for the inheritance of extended attributes
across fork() and exec().
The first simple scheme will allow privileged userspace to set
trusted extended attributes on pidfs inodes.
- Allow autonomous pidfs file handles
Various filesystems such as pidfs and drm support opening file
handles without having to require a file descriptor to identify the
filesystem. The filesystem are global single instances and can be
trivially identified solely on the information encoded in the file
handle.
This makes it possible to not have to keep or acquire a sentinal file
descriptor just to pass it to open_by_handle_at() to identify the
filesystem. That's especially useful when such sentinel file
descriptor cannot or should not be acquired.
For pidfs this means a file handle can function as full replacement
for storing a pid in a file. Instead a file handle can be stored and
reopened purely based on the file handle.
Such autonomous file handles can be opened with or without specifying
a a file descriptor. If no proper file descriptor is used the
FD_PIDFS_ROOT sentinel must be passed. This allows us to define
further special negative fd sentinels in the future.
Userspace can trivially test for support by trying to open the file
handle with an invalid file descriptor.
- Allow pidfds for reaped tasks with SCM_PIDFD messages
This is a logical continuation of the earlier work to create pidfds
for reaped tasks through the SO_PEERPIDFD socket option merged in
923ea4d448 ("Merge patch series "net, pidfs: enable handing out
pidfds for reaped sk->sk_peer_pid"").
- Two minor fixes:
* Fold fs_struct->{lock,seq} into a seqlock
* Don't bother with path_{get,put}() in unix_open_file()
* tag 'vfs-6.17-rc1.pidfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (37 commits)
don't bother with path_get()/path_put() in unix_open_file()
fold fs_struct->{lock,seq} into a seqlock
selftests: net: extend SCM_PIDFD test to cover stale pidfds
af_unix: enable handing out pidfds for reaped tasks in SCM_PIDFD
af_unix: stash pidfs dentry when needed
af_unix/scm: fix whitespace errors
af_unix: introduce and use scm_replace_pid() helper
af_unix: introduce unix_skb_to_scm helper
af_unix: rework unix_maybe_add_creds() to allow sleep
selftests/pidfd: decode pidfd file handles withou having to specify an fd
fhandle, pidfs: support open_by_handle_at() purely based on file handle
uapi/fcntl: add FD_PIDFS_ROOT
uapi/fcntl: add FD_INVALID
fcntl/pidfd: redefine PIDFD_SELF_THREAD_GROUP
uapi/fcntl: mark range as reserved
fhandle: reflow get_path_anchor()
pidfs: add pidfs_root_path() helper
fhandle: rename to get_path_anchor()
fhandle: hoist copy_from_user() above get_path_from_fd()
fhandle: raise FILEID_IS_DIR in handle_type
...
In Commit 1d8db6fd69 ("pidfs,
coredump: add PIDFD_INFO_COREDUMP"), the following code was added:
if (mask & PIDFD_INFO_COREDUMP) {
kinfo.mask |= PIDFD_INFO_COREDUMP;
kinfo.coredump_mask = READ_ONCE(pidfs_i(inode)->__pei.coredump_mask);
}
[...]
if (!(kinfo.mask & PIDFD_INFO_COREDUMP)) {
task_lock(task);
if (task->mm)
kinfo.coredump_mask = pidfs_coredump_mask(task->mm->flags);
task_unlock(task);
}
The second bit in particular looks off to me - the condition in essence
checks whether PIDFD_INFO_COREDUMP was **not** requested, and if so
fetches the coredump_mask in kinfo, since it's checking !(kinfo.mask &
PIDFD_INFO_COREDUMP), which is unconditionally set in the earlier hunk.
I'm tempted to assume the idea in the second hunk was to calculate the
coredump mask if one was requested but fetched in the first hunk, in
which case the check should be
if ((kinfo.mask & PIDFD_INFO_COREDUMP) && !(kinfo.coredump_mask))
which might be more legibly written as
if ((mask & PIDFD_INFO_COREDUMP) && !(kinfo.coredump_mask))
This could also instead be achieved by changing the first hunk to be:
if (mask & PIDFD_INFO_COREDUMP) {
kinfo.coredump_mask = READ_ONCE(pidfs_i(inode)->__pei.coredump_mask);
if (kinfo.coredump_mask)
kinfo.mask |= PIDFD_INFO_COREDUMP;
}
and the second hunk to:
if ((mask & PIDFD_INFO_COREDUMP) && !(kinfo.mask & PIDFD_INFO_COREDUMP)) {
task_lock(task);
if (task->mm) {
kinfo.coredump_mask = pidfs_coredump_mask(task->mm->flags);
kinfo.mask |= PIDFD_INFO_COREDUMP;
}
task_unlock(task);
}
However, when looking at this, the supposition that the second hunk
means to cover cases where the coredump info was requested but the first
hunk failed to get it starts getting doubtful, so apologies if I'm
completely off-base.
This patch addresses the issue by fixing the check in the second hunk.
Signed-off-by: Laura Brehm <laurabrehm@hey.com>
Link: https://lore.kernel.org/20250703120244.96908-3-laurabrehm@hey.com
Cc: brauner@kernel.org
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Ensure that we handle the case where task creation fails and pid->attr
was never accessed at all.
Signed-off-by: Christian Brauner <brauner@kernel.org>
Now that we have a way to persist information for pidfs dentries we can
start supporting extended attributes on pidfds. This will allow
userspace to attach meta information to tasks.
One natural extension would be to introduce a custom pidfs.* extended
attribute space and allow for the inheritance of extended attributes
across fork() and exec().
The first simple scheme will allow privileged userspace to set trusted
extended attributes on pidfs inodes.
Link: https://lore.kernel.org/20250618-work-pidfs-persistent-v2-12-98f3456fd552@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Now that we stash persistent information in struct pid there's no need
to play volatile games with pinning struct pid via dentries in pidfs.
Link: https://lore.kernel.org/20250618-work-pidfs-persistent-v2-8-98f3456fd552@kernel.org
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Persist exit and coredump information independent of whether anyone
currently holds a pidfd for the struct pid.
The current scheme allocated pidfs dentries on-demand repeatedly.
This scheme is reaching it's limits as it makes it impossible to pin
information that needs to be available after the task has exited or
coredumped and that should not be lost simply because the pidfd got
closed temporarily. The next opener should still see the stashed
information.
This is also a prerequisite for supporting extended attributes on
pidfds to allow attaching meta information to them.
If someone opens a pidfd for a struct pid a pidfs dentry is allocated
and stashed in pid->stashed. Once the last pidfd for the struct pid is
closed the pidfs dentry is released and removed from pid->stashed.
So if 10 callers create a pidfs dentry for the same struct pid
sequentially, i.e., each closing the pidfd before the other creates a
new one then a new pidfs dentry is allocated every time.
Because multiple tasks acquiring and releasing a pidfd for the same
struct pid can race with each another a task may still find a valid
pidfs entry from the previous task in pid->stashed and reuse it. Or it
might find a dead dentry in there and fail to reuse it and so stashes a
new pidfs dentry. Multiple tasks may race to stash a new pidfs dentry
but only one will succeed, the other ones will put their dentry.
The current scheme aims to ensure that a pidfs dentry for a struct pid
can only be created if the task is still alive or if a pidfs dentry
already existed before the task was reaped and so exit information has
been was stashed in the pidfs inode.
That's great except that it's buggy. If a pidfs dentry is stashed in
pid->stashed after pidfs_exit() but before __unhash_process() is called
we will return a pidfd for a reaped task without exit information being
available.
The pidfds_pid_valid() check does not guard against this race as it
doens't sync at all with pidfs_exit(). The pid_has_task() check might be
successful simply because we're before __unhash_process() but after
pidfs_exit().
Introduce a new scheme where the lifetime of information associated with
a pidfs entry (coredump and exit information) isn't bound to the
lifetime of the pidfs inode but the struct pid itself.
The first time a pidfs dentry is allocated for a struct pid a struct
pidfs_attr will be allocated which will be used to store exit and
coredump information.
If all pidfs for the pidfs dentry are closed the dentry and inode can be
cleaned up but the struct pidfs_attr will stick until the struct pid
itself is freed. This will ensure minimal memory usage while persisting
relevant information.
The new scheme has various advantages. First, it allows to close the
race where we end up handing out a pidfd for a reaped task for which no
exit information is available. Second, it minimizes memory usage.
Third, it allows to remove complex lifetime tracking via dentries when
registering a struct pid with pidfs. There's no need to get or put a
reference. Instead, the lifetime of exit and coredump information
associated with a struct pid is bound to the lifetime of struct pid
itself.
Link: https://lore.kernel.org/20250618-work-pidfs-persistent-v2-5-98f3456fd552@kernel.org
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Similar to commit 1ed95281c0 ("anon_inode: raise SB_I_NODEV and SB_I_NOEXEC"):
it shouldn't be possible to execute pidfds via
execveat(fd_anon_inode, "", NULL, NULL, AT_EMPTY_PATH)
so raise SB_I_NOEXEC so that no one gets any creative ideas.
Also raise SB_I_NODEV as we don't expect or support any devices on pidfs.
Link: https://lore.kernel.org/20250618-work-pidfs-persistent-v2-1-98f3456fd552@kernel.org
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
In systemd we spotted an issue after switching to ioctl(PIDFD_GET_INFO)
for obtaining pid number the pidfd refers to, that for processes
with a parent from outer pidns PIDFD_GET_INFO unexpectedly yields
-ESRCH [1]. It turned out that there's an arbitrary check blocking
this, which is not really sensible given getppid() happily returns
0 for such processes. Just drop the spurious check and userspace
ought to handle ppid == 0 properly everywhere.
[1] https://github.com/systemd/systemd/issues/37715
Fixes: cdda1f26e7 ("pidfd: add ioctl to retrieve pid info")
Signed-off-by: Mike Yuan <me@yhndnzj.com>
Link: https://lore.kernel.org/20250604150238.42664-1-me@yhndnzj.com
Cc: Christian Brauner <brauner@kernel.org>
Cc: Luca Boccassi <luca.boccassi@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
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Merge tag 'vfs-6.16-rc1.coredump' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs
Pull coredump updates from Christian Brauner:
"This adds support for sending coredumps over an AF_UNIX socket. It
also makes (implicit) use of the new SO_PEERPIDFD ability to hand out
pidfds for reaped peer tasks
The new coredump socket will allow userspace to not have to rely on
usermode helpers for processing coredumps and provides a saf way to
handle them instead of relying on super privileged coredumping helpers
This will also be significantly more lightweight since the kernel
doens't have to do a fork()+exec() for each crashing process to spawn
a usermodehelper. Instead the kernel just connects to the AF_UNIX
socket and userspace can process it concurrently however it sees fit.
Support for userspace is incoming starting with systemd-coredump
There's more work coming in that direction next cycle. The rest below
goes into some details and background
Coredumping currently supports two modes:
(1) Dumping directly into a file somewhere on the filesystem.
(2) Dumping into a pipe connected to a usermode helper process
spawned as a child of the system_unbound_wq or kthreadd
For simplicity I'm mostly ignoring (1). There's probably still some
users of (1) out there but processing coredumps in this way can be
considered adventurous especially in the face of set*id binaries
The most common option should be (2) by now. It works by allowing
userspace to put a string into /proc/sys/kernel/core_pattern like:
|/usr/lib/systemd/systemd-coredump %P %u %g %s %t %c %h
The "|" at the beginning indicates to the kernel that a pipe must be
used. The path following the pipe indicator is a path to a binary that
will be spawned as a usermode helper process. Any additional
parameters pass information about the task that is generating the
coredump to the binary that processes the coredump
In the example the core_pattern shown causes the kernel to spawn
systemd-coredump as a usermode helper. There's various conceptual
consequences of this (non-exhaustive list):
- systemd-coredump is spawned with file descriptor number 0 (stdin)
connected to the read-end of the pipe. All other file descriptors
are closed. That specifically includes 1 (stdout) and 2 (stderr).
This has already caused bugs because userspace assumed that this
cannot happen (Whether or not this is a sane assumption is
irrelevant)
- systemd-coredump will be spawned as a child of system_unbound_wq.
So it is not a child of any userspace process and specifically not
a child of PID 1. It cannot be waited upon and is in a weird hybrid
upcall which are difficult for userspace to control correctly
- systemd-coredump is spawned with full kernel privileges. This
necessitates all kinds of weird privilege dropping excercises in
userspace to make this safe
- A new usermode helper has to be spawned for each crashing process
This adds a new mode:
(3) Dumping into an AF_UNIX socket
Userspace can set /proc/sys/kernel/core_pattern to:
@/path/to/coredump.socket
The "@" at the beginning indicates to the kernel that an AF_UNIX
coredump socket will be used to process coredumps
The coredump socket must be located in the initial mount namespace.
When a task coredumps it opens a client socket in the initial network
namespace and connects to the coredump socket:
- The coredump server uses SO_PEERPIDFD to get a stable handle on the
connected crashing task. The retrieved pidfd will provide a stable
reference even if the crashing task gets SIGKILLed while generating
the coredump. That is a huge attack vector right now
- By setting core_pipe_limit non-zero userspace can guarantee that
the crashing task cannot be reaped behind it's back and thus
process all necessary information in /proc/<pid>. The SO_PEERPIDFD
can be used to detect whether /proc/<pid> still refers to the same
process
The core_pipe_limit isn't used to rate-limit connections to the
socket. This can simply be done via AF_UNIX socket directly
- The pidfd for the crashing task will contain information how the
task coredumps. The PIDFD_GET_INFO ioctl gained a new flag
PIDFD_INFO_COREDUMP which can be used to retreive the coredump
information
If the coredump gets a new coredump client connection the kernel
guarantees that PIDFD_INFO_COREDUMP information is available.
Currently the following information is provided in the new
@coredump_mask extension to struct pidfd_info:
* PIDFD_COREDUMPED is raised if the task did actually coredump
* PIDFD_COREDUMP_SKIP is raised if the task skipped coredumping
(e.g., undumpable)
* PIDFD_COREDUMP_USER is raised if this is a regular coredump and
doesn't need special care by the coredump server
* PIDFD_COREDUMP_ROOT is raised if the generated coredump should
be treated as sensitive and the coredump server should restrict
access to the generated coredump to sufficiently privileged
users"
* tag 'vfs-6.16-rc1.coredump' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
mips, net: ensure that SOCK_COREDUMP is defined
selftests/coredump: add tests for AF_UNIX coredumps
selftests/pidfd: add PIDFD_INFO_COREDUMP infrastructure
coredump: validate socket name as it is written
coredump: show supported coredump modes
pidfs, coredump: add PIDFD_INFO_COREDUMP
coredump: add coredump socket
coredump: reflow dump helpers a little
coredump: massage do_coredump()
coredump: massage format_corename()
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Merge tag 'vfs-6.16-rc1.pidfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs
Pull pidfs updates from Christian Brauner:
"Features:
- Allow handing out pidfds for reaped tasks for AF_UNIX SO_PEERPIDFD
socket option
SO_PEERPIDFD is a socket option that allows to retrieve a pidfd for
the process that called connect() or listen(). This is heavily used
to safely authenticate clients in userspace avoiding security bugs
due to pid recycling races (dbus, polkit, systemd, etc.)
SO_PEERPIDFD currently doesn't support handing out pidfds if the
sk->sk_peer_pid thread-group leader has already been reaped. In
this case it currently returns EINVAL. Userspace still wants to get
a pidfd for a reaped process to have a stable handle it can pass
on. This is especially useful now that it is possible to retrieve
exit information through a pidfd via the PIDFD_GET_INFO ioctl()'s
PIDFD_INFO_EXIT flag
Another summary has been provided by David Rheinsberg:
> A pidfd can outlive the task it refers to, and thus user-space
> must already be prepared that the task underlying a pidfd is
> gone at the time they get their hands on the pidfd. For
> instance, resolving the pidfd to a PID via the fdinfo must be
> prepared to read `-1`.
>
> Despite user-space knowing that a pidfd might be stale, several
> kernel APIs currently add another layer that checks for this. In
> particular, SO_PEERPIDFD returns `EINVAL` if the peer-task was
> already reaped, but returns a stale pidfd if the task is reaped
> immediately after the respective alive-check.
>
> This has the unfortunate effect that user-space now has two ways
> to check for the exact same scenario: A syscall might return
> EINVAL/ESRCH/... *or* the pidfd might be stale, even though
> there is no particular reason to distinguish both cases. This
> also propagates through user-space APIs, which pass on pidfds.
> They must be prepared to pass on `-1` *or* the pidfd, because
> there is no guaranteed way to get a stale pidfd from the kernel.
>
> Userspace must already deal with a pidfd referring to a reaped
> task as the task may exit and get reaped at any time will there
> are still many pidfds referring to it
In order to allow handing out reaped pidfd SO_PEERPIDFD needs to
ensure that PIDFD_INFO_EXIT information is available whenever a
pidfd for a reaped task is created by PIDFD_INFO_EXIT. The uapi
promises that reaped pidfds are only handed out if it is guaranteed
that the caller sees the exit information:
TEST_F(pidfd_info, success_reaped)
{
struct pidfd_info info = {
.mask = PIDFD_INFO_CGROUPID | PIDFD_INFO_EXIT,
};
/*
* Process has already been reaped and PIDFD_INFO_EXIT been set.
* Verify that we can retrieve the exit status of the process.
*/
ASSERT_EQ(ioctl(self->child_pidfd4, PIDFD_GET_INFO, &info), 0);
ASSERT_FALSE(!!(info.mask & PIDFD_INFO_CREDS));
ASSERT_TRUE(!!(info.mask & PIDFD_INFO_EXIT));
ASSERT_TRUE(WIFEXITED(info.exit_code));
ASSERT_EQ(WEXITSTATUS(info.exit_code), 0);
}
To hand out pidfds for reaped processes we thus allocate a pidfs
entry for the relevant sk->sk_peer_pid at the time the
sk->sk_peer_pid is stashed and drop it when the socket is
destroyed. This guarantees that exit information will always be
recorded for the sk->sk_peer_pid task and we can hand out pidfds
for reaped processes
- Hand a pidfd to the coredump usermode helper process
Give userspace a way to instruct the kernel to install a pidfd for
the crashing process into the process started as a usermode helper.
There's still tricky race-windows that cannot be easily or
sometimes not closed at all by userspace. There's various ways like
looking at the start time of a process to make sure that the
usermode helper process is started after the crashing process but
it's all very very brittle and fraught with peril
The crashed-but-not-reaped process can be killed by userspace
before coredump processing programs like systemd-coredump have had
time to manually open a PIDFD from the PID the kernel provides
them, which means they can be tricked into reading from an
arbitrary process, and they run with full privileges as they are
usermode helper processes
Even if that specific race-window wouldn't exist it's still the
safest and cleanest way to let the kernel provide the pidfd
directly instead of requiring userspace to do it manually. In
parallel with this commit we already have systemd adding support
for this in [1]
When the usermode helper process is forked we install a pidfd file
descriptor three into the usermode helper's file descriptor table
so it's available to the exec'd program
Since usermode helpers are either children of the system_unbound_wq
workqueue or kthreadd we know that the file descriptor table is
empty and can thus always use three as the file descriptor number
Note, that we'll install a pidfd for the thread-group leader even
if a subthread is calling do_coredump(). We know that task linkage
hasn't been removed yet and even if this @current isn't the actual
thread-group leader we know that the thread-group leader cannot be
reaped until
@current has exited
- Allow telling when a task has not been found from finding the wrong
task when creating a pidfd
We currently report EINVAL whenever a struct pid has no tasked
attached anymore thereby conflating two concepts:
(1) The task has already been reaped
(2) The caller requested a pidfd for a thread-group leader but the
pid actually references a struct pid that isn't used as a
thread-group leader
This is causing issues for non-threaded workloads as in where they
expect ESRCH to be reported, not EINVAL
So allow userspace to reliably distinguish between (1) and (2)
- Make it possible to detect when a pidfs entry would outlive the
struct pid it pinned
- Add a range of new selftests
Cleanups:
- Remove unneeded NULL check from pidfd_prepare() for passed struct
pid
- Avoid pointless reference count bump during release_task()
Fixes:
- Various fixes to the pidfd and coredump selftests
- Fix error handling for replace_fd() when spawning coredump usermode
helper"
* tag 'vfs-6.16-rc1.pidfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
pidfs: detect refcount bugs
coredump: hand a pidfd to the usermode coredump helper
coredump: fix error handling for replace_fd()
pidfs: move O_RDWR into pidfs_alloc_file()
selftests: coredump: Raise timeout to 2 minutes
selftests: coredump: Fix test failure for slow machines
selftests: coredump: Properly initialize pointer
net, pidfs: enable handing out pidfds for reaped sk->sk_peer_pid
pidfs: get rid of __pidfd_prepare()
net, pidfs: prepare for handing out pidfds for reaped sk->sk_peer_pid
pidfs: register pid in pidfs
net, pidfd: report EINVAL for ESRCH
release_task: kill the no longer needed get/put_pid(thread_pid)
pidfs: ensure consistent ENOENT/ESRCH reporting
exit: move wake_up_all() pidfd waiters into __unhash_process()
selftest/pidfd: add test for thread-group leader pidfd open for thread
pidfd: improve uapi when task isn't found
pidfd: remove unneeded NULL check from pidfd_prepare()
selftests/pidfd: adapt to recent changes
Extend the PIDFD_INFO_COREDUMP ioctl() with the new PIDFD_INFO_COREDUMP
mask flag. This adds the @coredump_mask field to struct pidfd_info.
When a task coredumps the kernel will provide the following information
to userspace in @coredump_mask:
* PIDFD_COREDUMPED is raised if the task did actually coredump.
* PIDFD_COREDUMP_SKIP is raised if the task skipped coredumping (e.g.,
undumpable).
* PIDFD_COREDUMP_USER is raised if this is a regular coredump and
doesn't need special care by the coredump server.
* PIDFD_COREDUMP_ROOT is raised if the generated coredump should be
treated as sensitive and the coredump server should restrict to the
generated coredump to sufficiently privileged users.
The kernel guarantees that by the time the connection is made the all
PIDFD_INFO_COREDUMP info is available.
Link: https://lore.kernel.org/20250516-work-coredump-socket-v8-5-664f3caf2516@kernel.org
Acked-by: Luca Boccassi <luca.boccassi@gmail.com>
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Reviewed-by: Jann Horn <jannh@google.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Since all pidfds must be O_RDWR currently enfore that directly in the
file allocation function itself instead of letting callers specify it.
Link: https://lore.kernel.org/20250414-work-coredump-v2-1-685bf231f828@kernel.org
Tested-by: Luca Boccassi <luca.boccassi@gmail.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Fold it into pidfd_prepare() and rename PIDFD_CLONE to PIDFD_STALE to
indicate that the passed pid might not have task linkage and no explicit
check for that should be performed.
Link: https://lore.kernel.org/20250425-work-pidfs-net-v2-3-450a19461e75@kernel.org
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: David Rheinsberg <david@readahead.eu>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Add simple helpers that allow a struct pid to be pinned via a pidfs
dentry/inode. If no pidfs dentry exists a new one will be allocated for
it. A reference is taken by pidfs on @pid. The reference must be
released via pidfs_put_pid().
This will allow AF_UNIX sockets to allocate a dentry for the peer
credentials pid at the time they are recorded where we know the task is
still alive. When the task gets reaped its exit status is guaranteed to
be recorded and a pidfd can be handed out for the reaped task.
Link: https://lore.kernel.org/20250425-work-pidfs-net-v2-1-450a19461e75@kernel.org
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: David Rheinsberg <david@readahead.eu>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This makes it easy to detect proper anonymous inodes and to ensure that
we can detect them in codepaths such as readahead().
Readahead on anonymous inodes didn't work because they didn't have a
proper mode. Now that they have we need to retain EINVAL being returned
otherwise LTP will fail.
We also need to ensure that ioctls aren't simply fired like they are for
regular files so things like inotify inodes continue to correctly call
their own ioctl handlers as in [1].
Reported-by: Xilin Wu <sophon@radxa.com>
Link: https://lore.kernel.org/3A9139D5CD543962+89831381-31b9-4392-87ec-a84a5b3507d8@radxa.com [1]
Link: https://lore.kernel.org/7a1a7076-ff6b-4cb0-94e7-7218a0a44028@sirena.org.uk
Signed-off-by: Christian Brauner <brauner@kernel.org>
So far pidfs did use it's own version. Just use the generic version.
We use our own wrappers because we're going to be implementing
properties soon.
Link: https://lore.kernel.org/20250407-work-anon_inode-v1-4-53a44c20d44e@kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
So far pidfs did use it's own version. Just use the generic version. We
use our own wrappers because we're going to be implementing our own
retrieval properties soon.
Link: https://lore.kernel.org/20250407-work-anon_inode-v1-2-53a44c20d44e@kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
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Merge tag 'vfs-6.15-rc1.pidfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs
Pull vfs pidfs updates from Christian Brauner:
- Allow retrieving exit information after a process has been reaped
through pidfds via the new PIDFD_INTO_EXIT extension for the
PIDFD_GET_INFO ioctl. Various tools need access to information about
a process/task even after it has already been reaped.
Pidfd polling allows waiting on either task exit or for a task to
have been reaped. The contract for PIDFD_INFO_EXIT is simply that
EPOLLHUP must be observed before exit information can be retrieved,
i.e., exit information is only provided once the task has been reaped
and then can be retrieved as long as the pidfd is open.
- Add PIDFD_SELF_{THREAD,THREAD_GROUP} sentinels allowing userspace to
forgo allocating a file descriptor for their own process. This is
useful in scenarios where users want to act on their own process
through pidfds and is akin to AT_FDCWD.
- Improve premature thread-group leader and subthread exec behavior
when polling on pidfds:
(1) During a multi-threaded exec by a subthread, i.e.,
non-thread-group leader thread, all other threads in the
thread-group including the thread-group leader are killed and the
struct pid of the thread-group leader will be taken over by the
subthread that called exec. IOW, two tasks change their TIDs.
(2) A premature thread-group leader exit means that the thread-group
leader exited before all of the other subthreads in the
thread-group have exited.
Both cases lead to inconsistencies for pidfd polling with
PIDFD_THREAD. Any caller that holds a PIDFD_THREAD pidfd to the
current thread-group leader may or may not see an exit notification
on the file descriptor depending on when poll is performed. If the
poll is performed before the exec of the subthread has concluded an
exit notification is generated for the old thread-group leader. If
the poll is performed after the exec of the subthread has concluded
no exit notification is generated for the old thread-group leader.
The correct behavior is to simply not generate an exit notification
on the struct pid of a subhthread exec because the struct pid is
taken over by the subthread and thus remains alive.
But this is difficult to handle because a thread-group may exit
premature as mentioned in (2). In that case an exit notification is
reliably generated but the subthreads may continue to run for an
indeterminate amount of time and thus also may exec at some point.
After this pull no exit notifications will be generated for a
PIDFD_THREAD pidfd for a thread-group leader until all subthreads
have been reaped. If a subthread should exec before no exit
notification will be generated until that task exits or it creates
subthreads and repeates the cycle.
This means an exit notification indicates the ability for the father
to reap the child.
* tag 'vfs-6.15-rc1.pidfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (25 commits)
selftests/pidfd: third test for multi-threaded exec polling
selftests/pidfd: second test for multi-threaded exec polling
selftests/pidfd: first test for multi-threaded exec polling
pidfs: improve multi-threaded exec and premature thread-group leader exit polling
pidfs: ensure that PIDFS_INFO_EXIT is available
selftests/pidfd: add seventh PIDFD_INFO_EXIT selftest
selftests/pidfd: add sixth PIDFD_INFO_EXIT selftest
selftests/pidfd: add fifth PIDFD_INFO_EXIT selftest
selftests/pidfd: add fourth PIDFD_INFO_EXIT selftest
selftests/pidfd: add third PIDFD_INFO_EXIT selftest
selftests/pidfd: add second PIDFD_INFO_EXIT selftest
selftests/pidfd: add first PIDFD_INFO_EXIT selftest
selftests/pidfd: expand common pidfd header
pidfs/selftests: ensure correct headers for ioctl handling
selftests/pidfd: fix header inclusion
pidfs: allow to retrieve exit information
pidfs: record exit code and cgroupid at exit
pidfs: use private inode slab cache
pidfs: move setting flags into pidfs_alloc_file()
pidfd: rely on automatic cleanup in __pidfd_prepare()
...
This is another attempt trying to make pidfd polling for multi-threaded
exec and premature thread-group leader exit consistent.
A quick recap of these two cases:
(1) During a multi-threaded exec by a subthread, i.e., non-thread-group
leader thread, all other threads in the thread-group including the
thread-group leader are killed and the struct pid of the
thread-group leader will be taken over by the subthread that called
exec. IOW, two tasks change their TIDs.
(2) A premature thread-group leader exit means that the thread-group
leader exited before all of the other subthreads in the thread-group
have exited.
Both cases lead to inconsistencies for pidfd polling with PIDFD_THREAD.
Any caller that holds a PIDFD_THREAD pidfd to the current thread-group
leader may or may not see an exit notification on the file descriptor
depending on when poll is performed. If the poll is performed before the
exec of the subthread has concluded an exit notification is generated
for the old thread-group leader. If the poll is performed after the exec
of the subthread has concluded no exit notification is generated for the
old thread-group leader.
The correct behavior would be to simply not generate an exit
notification on the struct pid of a subhthread exec because the struct
pid is taken over by the subthread and thus remains alive.
But this is difficult to handle because a thread-group may exit
prematurely as mentioned in (2). In that case an exit notification is
reliably generated but the subthreads may continue to run for an
indeterminate amount of time and thus also may exec at some point.
So far there was no way to distinguish between (1) and (2) internally.
This tiny series tries to address this problem by discarding
PIDFD_THREAD notification on premature thread-group leader exit.
If that works correctly then no exit notifications are generated for a
PIDFD_THREAD pidfd for a thread-group leader until all subthreads have
been reaped. If a subthread should exec aftewards no exit notification
will be generated until that task exits or it creates subthreads and
repeates the cycle.
Co-Developed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/20250320-work-pidfs-thread_group-v4-1-da678ce805bf@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
When we currently create a pidfd we check that the task hasn't been
reaped right before we create the pidfd. But it is of course possible
that by the time we return the pidfd to userspace the task has already
been reaped since we don't check again after having created a dentry for
it.
This was fine until now because that race was meaningless. But now that
we provide PIDFD_INFO_EXIT it is a problem because it is possible that
the kernel returns a reaped pidfd and it depends on the race whether
PIDFD_INFO_EXIT information is available. This depends on if the task
gets reaped before or after a dentry has been attached to struct pid.
Make this consistent and only returned pidfds for reaped tasks if
PIDFD_INFO_EXIT information is available. This is done by performing
another check whether the task has been reaped right after we attached a
dentry to struct pid.
Since pidfs_exit() is called before struct pid's task linkage is removed
the case where the task got reaped but a dentry was already attached to
struct pid and exit information was recorded and published can be
handled correctly. In that case we do return a pidfd for a reaped task
like we would've before.
Link: https://lore.kernel.org/r/20250316-kabel-fehden-66bdb6a83436@brauner
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Some tools like systemd's jounral need to retrieve the exit and cgroup
information after a process has already been reaped. This can e.g.,
happen when retrieving a pidfd via SCM_PIDFD or SCM_PEERPIDFD.
Link: https://lore.kernel.org/r/20250305-work-pidfs-kill_on_last_close-v3-6-c8c3d8361705@kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Record the exit code and cgroupid in release_task() and stash in struct
pidfs_exit_info so it can be retrieved even after the task has been
reaped.
Link: https://lore.kernel.org/r/20250305-work-pidfs-kill_on_last_close-v3-5-c8c3d8361705@kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Introduce a private inode slab cache for pidfs. In follow-up patches
pidfs will gain the ability to provide exit information to userspace
after the task has been reaped. This means storing exit information even
after the task has already been released and struct pid's task linkage
is gone. Store that information alongside the inode.
Link: https://lore.kernel.org/r/20250305-work-pidfs-kill_on_last_close-v3-4-c8c3d8361705@kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Linus Torvalds