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writeback: prevent memory cgroup release in writeback module 

In the near future, a folio will no longer pin its corresponding memory
cgroup.  To ensure safety, it will only be appropriate to hold the rcu
read lock or acquire a reference to the memory cgroup returned by
folio_memcg(), thereby preventing it from being released.

In the current patch, the function get_mem_cgroup_css_from_folio() and the
rcu read lock are employed to safeguard against the release of the memory
cgroup.

This serves as a preparatory measure for the reparenting of the
LRU pages.

Link: https://lore.kernel.org/645f99bc344575417f67def3744f975596df2793.1772711148.git.zhengqi.arch@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Allen Pais <apais@linux.microsoft.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Chen Ridong <chenridong@huawei.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Imran Khan <imran.f.khan@oracle.com>
Cc: Kamalesh Babulal <kamalesh.babulal@oracle.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam Howlett <Liam.Howlett@oracle.com>
Cc: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Wei Xu <weixugc@google.com>
Cc: Yosry Ahmed <yosry@kernel.org>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
master
Muchun Song 2026-03-05 19:52:28 +08:00 committed by Andrew Morton
parent d10adce2c1
commit 49717c7bd6
4 changed files with 29 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

22
fs/fs-writeback.c
View File

@ -280,15 +280,13 @@ void __inode_attach_wb(struct inode *inode, struct folio *folio)
if (inode_cgwb_enabled(inode)) {
struct cgroup_subsys_state *memcg_css;
if (folio) {
memcg_css = mem_cgroup_css_from_folio(folio);
wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
} else {
/* must pin memcg_css, see wb_get_create() */
/* must pin memcg_css, see wb_get_create() */
if (folio)
memcg_css = get_mem_cgroup_css_from_folio(folio);
else
memcg_css = task_get_css(current, memory_cgrp_id);
wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
css_put(memcg_css);
}
wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
css_put(memcg_css);
}
if (!wb)
@ -979,16 +977,16 @@ void wbc_account_cgroup_owner(struct writeback_control *wbc, struct folio *folio
if (!wbc->wb || wbc->no_cgroup_owner)
return;
css = mem_cgroup_css_from_folio(folio);
css = get_mem_cgroup_css_from_folio(folio);
/* dead cgroups shouldn't contribute to inode ownership arbitration */
if (!css_is_online(css))
return;
goto out;
id = css->id;
if (id == wbc->wb_id) {
wbc->wb_bytes += bytes;
return;
goto out;
}
if (id == wbc->wb_lcand_id)
@ -1001,6 +999,8 @@ void wbc_account_cgroup_owner(struct writeback_control *wbc, struct folio *folio
wbc->wb_tcand_bytes += bytes;
else
wbc->wb_tcand_bytes -= min(bytes, wbc->wb_tcand_bytes);
out:
css_put(css);
}
EXPORT_SYMBOL_GPL(wbc_account_cgroup_owner);

9
include/linux/memcontrol.h
View File

@ -894,7 +894,7 @@ static inline bool mm_match_cgroup(struct mm_struct *mm,
return match;
}
struct cgroup_subsys_state *mem_cgroup_css_from_folio(struct folio *folio);
struct cgroup_subsys_state *get_mem_cgroup_css_from_folio(struct folio *folio);
ino_t page_cgroup_ino(struct page *page);
static inline bool mem_cgroup_online(struct mem_cgroup *memcg)
@ -1563,9 +1563,14 @@ static inline void mem_cgroup_track_foreign_dirty(struct folio *folio,
if (mem_cgroup_disabled())
return;
if (!folio_memcg_charged(folio))
return;
rcu_read_lock();
memcg = folio_memcg(folio);
if (unlikely(memcg && &memcg->css != wb->memcg_css))
if (unlikely(&memcg->css != wb->memcg_css))
mem_cgroup_track_foreign_dirty_slowpath(folio, wb);
rcu_read_unlock();
}
void mem_cgroup_flush_foreign(struct bdi_writeback *wb);

3
include/trace/events/writeback.h
View File

@ -294,7 +294,10 @@ TRACE_EVENT(track_foreign_dirty,
__entry->ino = inode ? inode->i_ino : 0;
__entry->memcg_id = wb->memcg_css->id;
__entry->cgroup_ino = __trace_wb_assign_cgroup(wb);
rcu_read_lock();
__entry->page_cgroup_ino = cgroup_ino(folio_memcg(folio)->css.cgroup);
rcu_read_unlock();
),
TP_printk("bdi %s[%llu]: ino=%lu memcg_id=%u cgroup_ino=%lu page_cgroup_ino=%lu",

14
mm/memcontrol.c
View File

@ -243,7 +243,7 @@ DEFINE_STATIC_KEY_FALSE(memcg_bpf_enabled_key);
EXPORT_SYMBOL(memcg_bpf_enabled_key);
/**
* mem_cgroup_css_from_folio - css of the memcg associated with a folio
* get_mem_cgroup_css_from_folio - acquire a css of the memcg associated with a folio
* @folio: folio of interest
*
* If memcg is bound to the default hierarchy, css of the memcg associated
@ -253,14 +253,16 @@ EXPORT_SYMBOL(memcg_bpf_enabled_key);
* If memcg is bound to a traditional hierarchy, the css of root_mem_cgroup
* is returned.
*/
struct cgroup_subsys_state *mem_cgroup_css_from_folio(struct folio *folio)
struct cgroup_subsys_state *get_mem_cgroup_css_from_folio(struct folio *folio)
{
struct mem_cgroup *memcg = folio_memcg(folio);
struct mem_cgroup *memcg;
if (!memcg || !cgroup_subsys_on_dfl(memory_cgrp_subsys))
memcg = root_mem_cgroup;
if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
return &root_mem_cgroup->css;
return &memcg->css;
memcg = get_mem_cgroup_from_folio(folio);
return memcg ? &memcg->css : &root_mem_cgroup->css;
}
/**