archives/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-03-14 00:56:20 +01:00
Code Issues Projects Releases Packages Wiki Activity Actions
Linux kernel source tree
1364812 commits 1 branch 922 tags 8.5 GiB
Find a file
Shakeel Butt dfe25fbaed cgroup: llist: avoid memory tears for llist_node 
Before the commit 36df6e3dbd ("cgroup: make css_rstat_updated nmi
safe"), the struct llist_node is expected to be private to the one
inserting the node to the lockless list or the one removing the node
from the lockless list. After the mentioned commit, the llist_node in
the rstat code is per-cpu shared between the stacked contexts i.e.
process, softirq, hardirq & nmi. It is possible the compiler may tear
the loads or stores of llist_node. Let's avoid that.

KCSAN reported the following race:

 Reported by Kernel Concurrency Sanitizer on:
 CPU: 60 UID: 0 PID: 5425 ... 6.16.0-rc3-next-20250626 #1 NONE
 Tainted: [E]=UNSIGNED_MODULE
 Hardware name: ...
 ==================================================================
 ==================================================================
 BUG: KCSAN: data-race in css_rstat_flush / css_rstat_updated
 write to 0xffffe8fffe1c85f0 of 8 bytes by task 1061 on cpu 1:
  css_rstat_flush+0x1b8/0xeb0
  __mem_cgroup_flush_stats+0x184/0x190
  flush_memcg_stats_dwork+0x22/0x50
  process_one_work+0x335/0x630
  worker_thread+0x5f1/0x8a0
  kthread+0x197/0x340
  ret_from_fork+0xd3/0x110
  ret_from_fork_asm+0x11/0x20
 read to 0xffffe8fffe1c85f0 of 8 bytes by task 3551 on cpu 15:
  css_rstat_updated+0x81/0x180
  mod_memcg_lruvec_state+0x113/0x2d0
  __mod_lruvec_state+0x3d/0x50
  lru_add+0x21e/0x3f0
  folio_batch_move_lru+0x80/0x1b0
  __folio_batch_add_and_move+0xd7/0x160
  folio_add_lru_vma+0x42/0x50
  do_anonymous_page+0x892/0xe90
  __handle_mm_fault+0xfaa/0x1520
  handle_mm_fault+0xdc/0x350
  do_user_addr_fault+0x1dc/0x650
  exc_page_fault+0x5c/0x110
  asm_exc_page_fault+0x22/0x30
 value changed: 0xffffe8fffe18e0d0 -> 0xffffe8fffe1c85f0

$ ./scripts/faddr2line vmlinux css_rstat_flush+0x1b8/0xeb0
css_rstat_flush+0x1b8/0xeb0:
init_llist_node at include/linux/llist.h:86
(inlined by) llist_del_first_init at include/linux/llist.h:308
(inlined by) css_process_update_tree at kernel/cgroup/rstat.c:148
(inlined by) css_rstat_updated_list at kernel/cgroup/rstat.c:258
(inlined by) css_rstat_flush at kernel/cgroup/rstat.c:389

$ ./scripts/faddr2line vmlinux css_rstat_updated+0x81/0x180
css_rstat_updated+0x81/0x180:
css_rstat_updated at kernel/cgroup/rstat.c:90 (discriminator 1)

These are expected race and a simple READ_ONCE/WRITE_ONCE resolves these
reports. However let's add comments to explain the race and the need for
memory barriers if stronger guarantees are needed.

More specifically the rstat updater and the flusher can race and cause a
scenario where the stats updater skips adding the css to the lockless
list but the flusher might not see those updates done by the skipped
updater. This is benign race and the subsequent flusher will flush those
stats and at the moment there aren't any rstat users which are not fine
with this kind of race. However some future user might want more
stricter guarantee, so let's add appropriate comments to ease the job of
future users.

Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Fixes: 36df6e3dbd ("cgroup: make css_rstat_updated nmi safe")
Signed-off-by: Tejun Heo <tj@kernel.org>
2025-07-17 07:41:56 -10:00
arch Xtensa updates for v6.16 2025-06-03 09:05:01 -07:00
block cgroup: Changes for v6.16 2025-05-27 20:59:53 -07:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto EFI updates for v6.16 2025-05-30 12:42:57 -07:00
Documentation Documentation: cgroup: add section explaining controller availability 2025-06-09 08:05:13 -10:00
drivers hid-for-linus-2025060301 2025-06-03 10:34:36 -07:00
fs - The 2 patch series "zram: support algorithm-specific parameters" from 2025-06-02 16:00:26 -07:00
include cgroup: llist: avoid memory tears for llist_node 2025-07-17 07:41:56 -10:00
init - The 2 patch series "zram: support algorithm-specific parameters" from 2025-06-02 16:00:26 -07:00
io_uring Networking changes for 6.16. 2025-05-28 15:24:36 -07:00
ipc - The 3 patch series "hung_task: extend blocking task stacktrace dump to 2025-05-31 19:12:53 -07:00
kernel cgroup: llist: avoid memory tears for llist_node 2025-07-17 07:41:56 -10:00
lib bitmap-for-6.16 2025-06-03 07:39:23 -07:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm memcg: cgroup: call css_rstat_updated irrespective of in_nmi() 2025-06-17 10:01:47 -10:00
net vfs-6.16-rc1.netfs 2025-06-02 15:04:06 -07:00
rust - The 2 patch series "zram: support algorithm-specific parameters" from 2025-06-02 16:00:26 -07:00
samples - The 3 patch series "hung_task: extend blocking task stacktrace dump to 2025-05-31 19:12:53 -07:00
scripts - The 2 patch series "zram: support algorithm-specific parameters" from 2025-06-02 16:00:26 -07:00
security require gcc-8 and binutils-2.30 2025-05-31 08:16:52 -07:00
sound sound updates for 6.16-rc1 2025-05-27 15:05:18 -07:00
tools selftests: cgroup: Fix missing newline in test_zswap_writeback_one 2025-07-12 07:35:30 -10:00
usr usr/include: openrisc: don't HDRTEST bpf_perf_event.h 2025-05-12 15:03:17 +09:00
virt Merge branch 'kvm-lockdep-common' into HEAD 2025-05-28 06:29:17 -04:00
.clang-format Linux 6.15-rc5 2025-05-06 16:39:25 +10:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: Retire Ralf Baechle 2024-11-12 15:48:59 +01:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore .gitignore: ignore Python compiled bytecode 2025-04-24 10:12:46 -06:00
.mailmap - The 3 patch series "hung_task: extend blocking task stacktrace dump to 2025-05-31 19:12:53 -07:00
.pylintrc docs: add a .pylintrc file with sys path for docs scripts 2025-04-09 12:10:33 -06:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS Update Christoph's Email address and make it consistent 2025-05-12 23:50:31 -07:00
Kbuild drm: ensure drm headers are self-contained and pass kernel-doc 2025-02-12 10:44:43 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS hwmon updates for v6.16 2025-06-03 09:11:26 -07:00
Makefile A moderately busy cycle for documentation this time around: 2025-05-27 11:22:19 -07:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

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

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.