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charset=us-ascii Content-Disposition: inline In-Reply-To: <20240424125940.2410718-1-leitao@debian.org> X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 8E29940010 X-Stat-Signature: uycis87twb3cztedf8h1jcuot5jsbrqy X-Rspam-User: X-HE-Tag: 1713964760-765103 X-HE-Meta: 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 BZJJuSfI 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Apr 24, 2024 at 05:59:39AM -0700, Breno Leitao wrote: > 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) > > > 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) > > > 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. > > Suggested-by: Shakeel Butt > Signed-off-by: Breno Leitao Acked-by: Johannes Weiner