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Gerd Rausch 826c1004d4 net/rds: rds_tcp_conn_path_shutdown must not discard messages
RDS/TCP differs from RDS/RDMA in that message acknowledgment
is done based on TCP sequence numbers:
As soon as the last byte of a message has been acknowledged by the
TCP stack of a peer, rds_tcp_write_space() goes on to discard
prior messages from the send queue.

Which is fine, for as long as the receiver never throws any messages
away.

The dequeuing of messages in RDS/TCP is done either from the
"sk_data_ready" callback pointing to rds_tcp_data_ready()
(the most common case), or from the receive worker pointing
to rds_tcp_recv_path() which is called for as long as the
connection is "RDS_CONN_UP".

However, as soon as rds_conn_path_drop() is called for whatever reason,
including "DR_USER_RESET", "cp_state" transitions to "RDS_CONN_ERROR",
and rds_tcp_restore_callbacks() ends up restoring the callbacks
and thereby disabling message receipt.

So messages already acknowledged to the sender were dropped.

Furthermore, the "->shutdown" callback was always called
with an invalid parameter ("RCV_SHUTDOWN | SEND_SHUTDOWN == 3"),
instead of the correct pre-increment value ("SHUT_RDWR == 2").
inet_shutdown() returns "-EINVAL" in such cases, rendering
this call a NOOP.

So we change rds_tcp_conn_path_shutdown() to do the proper
"->shutdown(SHUT_WR)" call in order to signal EOF to the peer
and make it transition to "TCP_CLOSE_WAIT" (RFC 793).

This should make the peer also enter rds_tcp_conn_path_shutdown()
and do the same.

This allows us to dequeue all messages already received
and acknowledged to the peer.
We do so, until we know that the receive queue no longer has data
(skb_queue_empty()) and that we couldn't have any data
in flight anymore, because the socket transitioned to
any of the states "CLOSING", "TIME_WAIT", "CLOSE_WAIT",
"LAST_ACK", or "CLOSE" (RFC 793).

However, if we do just that, we suddenly see duplicate RDS
messages being delivered to the application.
So what gives?

Turns out that with MPRDS and its multitude of backend connections,
retransmitted messages ("RDS_FLAG_RETRANSMITTED") can outrace
the dequeuing of their original counterparts.

And the duplicate check implemented in rds_recv_local() only
discards duplicates if flag "RDS_FLAG_RETRANSMITTED" is set.

Rather curious, because a duplicate is a duplicate; it shouldn't
matter which copy is looked at and delivered first.

To avoid this entire situation, we simply make the sender discard
messages from the send-queue right from within
rds_tcp_conn_path_shutdown().  Just like rds_tcp_write_space() would
have done, were it called in time or still called.

This makes sure that we no longer have messages that we know
the receiver already dequeued sitting in our send-queue,
and therefore avoid the entire "RDS_FLAG_RETRANSMITTED" fiasco.

Now we got rid of the duplicate RDS message delivery, but we
still run into cases where RDS messages are dropped.

This time it is due to the delayed setting of the socket-callbacks
in rds_tcp_accept_one() via either rds_tcp_reset_callbacks()
or rds_tcp_set_callbacks().

By the time rds_tcp_accept_one() gets there, the socket
may already have transitioned into state "TCP_CLOSE_WAIT",
but rds_tcp_state_change() was never called.

Subsequently, "->shutdown(SHUT_WR)" did not happen either.
So the peer ends up getting stuck in state "TCP_FIN_WAIT2".

We fix that by checking for states "TCP_CLOSE_WAIT", "TCP_LAST_ACK",
or "TCP_CLOSE" and drop the freshly accepted socket in that case.

This problem is observable by running "rds-stress --reset"
frequently on either of the two sides of a RDS connection,
or both while other "rds-stress" processes are exchanging data.
Those "rds-stress" processes reported out-of-sequence
errors, with the expected sequence number being smaller
than the one actually received (due to the dropped messages).

Signed-off-by: Gerd Rausch <gerd.rausch@oracle.com>
Signed-off-by: Allison Henderson <allison.henderson@oracle.com>
Link: https://patch.msgid.link/20260203055723.1085751-4-achender@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2026-02-04 20:46:38 -08:00
Documentation Some more changes, including pulls from drivers: 2026-02-04 20:31:05 -08:00
LICENSES LICENSES: Add modern form of the LGPL-2.1 tags to the usage guide section 2025-10-22 07:58:19 +02:00
arch Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2026-01-29 17:28:54 -08:00
block block-6.19-20260122 2026-01-23 12:53:56 -08:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: authencesn - reject too-short AAD (assoclen<8) to match ESP/ESN spec 2026-01-20 14:38:48 +08:00
drivers ovpn: Replace use of system_wq with system_percpu_wq 2026-02-04 20:41:38 -08:00
fs for-6.19-rc7-tag 2026-01-29 09:07:17 -08:00
include net/iucv: clean up iucv kernel-doc warnings 2026-02-04 20:39:58 -08:00
init Significant patch series in this pull request: 2025-12-06 14:01:20 -08:00
io_uring io_uring-6.19-20260122 2026-01-23 12:51:00 -08:00
ipc Significant patch series in this pull request: 2025-12-06 14:01:20 -08:00
kernel tracing fixes for v6.19: 2026-01-24 17:18:57 -08:00
lib lib/crypto: sha1: Remove low-level functions from API 2026-01-27 15:47:41 -08:00
mm slab fix for 6.19-rc7 2026-01-21 09:19:15 -08:00
net net/rds: rds_tcp_conn_path_shutdown must not discard messages 2026-02-04 20:46:38 -08:00
rust Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2026-01-29 17:28:54 -08:00
samples samples/ftrace: Adjust LoongArch register restore order in direct calls 2025-12-31 15:19:25 +08:00
scripts tracing fixes for v6.19: 2026-01-24 17:18:57 -08:00
security keys/trusted_keys: fix handle passed to tpm_buf_append_name during unseal 2026-01-25 19:03:45 +02:00
sound ALSA: hda/realtek: ALC269 fixup for Lenovo Yoga Book 9i 13IRU8 audio 2026-01-22 13:33:41 +01:00
tools selftests: mptcp: join: no SKIP mark for group checks 2026-02-04 18:45:34 -08:00
usr initramfs: add gen_init_cpio to hostprogs unconditionally 2025-11-26 21:55:40 +01:00
virt KVM fixes for 6.19-rc1 2025-12-18 18:38:45 +01:00
.clang-format s390/pci: Fix cyclic dead-lock in zpci_zdev_put() and zpci_scan_devices() 2025-12-14 11:03:58 +01:00
.clippy.toml rust: clean Rust 1.88.0's warning about `clippy::disallowed_macros` configuration 2025-05-07 00:11:47 +02:00
.cocciconfig
.editorconfig
.get_maintainer.ignore MAINTAINERS: remove Alyssa Rosenzweig 2025-09-18 21:17:31 +02:00
.gitattributes
.gitignore rust: kbuild: add proc macro library support 2025-11-24 17:15:36 +01:00
.mailmap soc: fixes for 6.19, part 2 2026-01-21 09:34:45 -08:00
.pylintrc docs: Move the python libraries to tools/lib/python 2025-11-18 09:22:40 -07:00
.rustfmt.toml
COPYING
CREDITS net: ethernet: neterion: s2io: remove unused driver 2026-01-28 20:08:07 -08:00
Kbuild sched: Make migrate_{en,dis}able() inline 2025-09-25 09:57:16 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS dt-bindings: ptp: Add amazon,vmclock 2026-02-02 18:06:00 -08:00
Makefile Linux 6.19-rc7 2026-01-25 14:11:24 -08:00
README README: restructure with role-based documentation and guidelines 2025-11-29 08:40:33 -07:00

README

Linux kernel
============

The Linux kernel is the core of any Linux operating system. It manages hardware,
system resources, and provides the fundamental services for all other software.

Quick Start
-----------

* Report a bug: See Documentation/admin-guide/reporting-issues.rst
* Get the latest kernel: https://kernel.org
* Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst
* Join the community: https://lore.kernel.org/

Essential Documentation
-----------------------

All users should be familiar with:

* Building requirements: Documentation/process/changes.rst
* Code of Conduct: Documentation/process/code-of-conduct.rst
* License: See COPYING

Documentation can be built with make htmldocs or viewed online at:
https://www.kernel.org/doc/html/latest/


Who Are You?
============

Find your role below:

* New Kernel Developer - Getting started with kernel development
* Academic Researcher - Studying kernel internals and architecture
* Security Expert - Hardening and vulnerability analysis
* Backport/Maintenance Engineer - Maintaining stable kernels
* System Administrator - Configuring and troubleshooting
* Maintainer - Leading subsystems and reviewing patches
* Hardware Vendor - Writing drivers for new hardware
* Distribution Maintainer - Packaging kernels for distros


For Specific Users
==================

New Kernel Developer
--------------------

Welcome! Start your kernel development journey here:

* Getting Started: Documentation/process/development-process.rst
* Your First Patch: Documentation/process/submitting-patches.rst
* Coding Style: Documentation/process/coding-style.rst
* Build System: Documentation/kbuild/index.rst
* Development Tools: Documentation/dev-tools/index.rst
* Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst
* Core APIs: Documentation/core-api/index.rst

Academic Researcher
-------------------

Explore the kernel's architecture and internals:

* Researcher Guidelines: Documentation/process/researcher-guidelines.rst
* Memory Management: Documentation/mm/index.rst
* Scheduler: Documentation/scheduler/index.rst
* Networking Stack: Documentation/networking/index.rst
* Filesystems: Documentation/filesystems/index.rst
* RCU (Read-Copy Update): Documentation/RCU/index.rst
* Locking Primitives: Documentation/locking/index.rst
* Power Management: Documentation/power/index.rst

Security Expert
---------------

Security documentation and hardening guides:

* Security Documentation: Documentation/security/index.rst
* LSM Development: Documentation/security/lsm-development.rst
* Self Protection: Documentation/security/self-protection.rst
* Reporting Vulnerabilities: Documentation/process/security-bugs.rst
* CVE Procedures: Documentation/process/cve.rst
* Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst
* Security Features: Documentation/userspace-api/seccomp_filter.rst

Backport/Maintenance Engineer
-----------------------------

Maintain and stabilize kernel versions:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* Backporting Guide: Documentation/process/backporting.rst
* Applying Patches: Documentation/process/applying-patches.rst
* Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git for Maintainers: Documentation/maintainer/configure-git.rst

System Administrator
--------------------

Configure, tune, and troubleshoot Linux systems:

* Admin Guide: Documentation/admin-guide/index.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst
* Tracing/Debugging: Documentation/trace/index.rst
* Performance Security: Documentation/admin-guide/perf-security.rst
* Hardware Monitoring: Documentation/hwmon/index.rst

Maintainer
----------

Lead kernel subsystems and manage contributions:

* Maintainer Handbook: Documentation/maintainer/index.rst
* Pull Requests: Documentation/maintainer/pull-requests.rst
* Managing Patches: Documentation/maintainer/modifying-patches.rst
* Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst
* Development Process: Documentation/process/maintainer-handbooks.rst
* Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git Configuration: Documentation/maintainer/configure-git.rst

Hardware Vendor
---------------

Write drivers and support new hardware:

* Driver API Guide: Documentation/driver-api/index.rst
* Driver Model: Documentation/driver-api/driver-model/driver.rst
* Device Drivers: Documentation/driver-api/infrastructure.rst
* Bus Types: Documentation/driver-api/driver-model/bus.rst
* Device Tree Bindings: Documentation/devicetree/bindings/
* Power Management: Documentation/driver-api/pm/index.rst
* DMA API: Documentation/core-api/dma-api.rst

Distribution Maintainer
-----------------------

Package and distribute the kernel:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* ABI Documentation: Documentation/ABI/README
* Kernel Configuration: Documentation/kbuild/kconfig.rst
* Module Signing: Documentation/admin-guide/module-signing.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst



Communication and Support
=========================

* Mailing Lists: https://lore.kernel.org/
* IRC: #kernelnewbies on irc.oftc.net
* Bugzilla: https://bugzilla.kernel.org/
* MAINTAINERS file: Lists subsystem maintainers and mailing lists
* Email Clients: Documentation/process/email-clients.rst