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A data-race issue in memcg rstat occurs when two distinct code paths
access the same 4-byte region concurrently. KCSAN detection triggers the
following BUG as a result.
BUG: KCSAN: data-race in __count_memcg_events / mem_cgroup_css_rstat_flush
write to 0xffffe8ffff98e300 of 4 bytes by task 5274 on cpu 17:
mem_cgroup_css_rstat_flush (mm/memcontrol.c:5850)
cgroup_rstat_flush_locked (kernel/cgroup/rstat.c:243 (discriminator 7))
cgroup_rstat_flush (./include/linux/spinlock.h:401 kernel/cgroup/rstat.c:278)
mem_cgroup_flush_stats.part.0 (mm/memcontrol.c:767)
memory_numa_stat_show (mm/memcontrol.c:6911)
<snip>
read to 0xffffe8ffff98e300 of 4 bytes by task 410848 on cpu 27:
__count_memcg_events (mm/memcontrol.c:725 mm/memcontrol.c:962)
count_memcg_event_mm.part.0 (./include/linux/memcontrol.h:1097 ./include/linux/memcontrol.h:1120)
handle_mm_fault (mm/memory.c:5483 mm/memory.c:5622)
<snip>
value changed: 0x00000029 -> 0x00000000
The race occurs because two code paths access the same "stats_updates"
location. Although "stats_updates" is a per-CPU variable, it is remotely
accessed by another CPU at
cgroup_rstat_flush_locked()->mem_cgroup_css_rstat_flush(), leading to the
data race mentioned.
Considering that memcg_rstat_updated() is in the hot code path, adding a
lock to protect it may not be desirable, especially since this variable
pertains solely to statistics.
Therefore, annotating accesses to stats_updates with READ/WRITE_ONCE() can
prevent KCSAN splats and potential partial reads/writes.
Link: https://lkml.kernel.org/r/20240424125940.2410718-1-leitao@debian.org
Fixes:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| 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.