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From: Shakeel Butt To: Breno Leitao Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Andrew Morton , paulmck@kernel.org, "open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" , "open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" , open list Subject: Re: [PATCH] mm: memcg: use READ_ONCE()/WRITE_ONCE() to access stock->nr_pages Message-ID: <7hm5jb6sxg3hd2qtp3qpei6mskdva6kseik6jlna4dlpliangc@m4xs3i2cgg34> References: <20240501095420.679208-1-leitao@debian.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240501095420.679208-1-leitao@debian.org> X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 38650A0013 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: 58f15kcrat3zykymo8qyquut51c6ywq9 X-HE-Tag: 1714596471-891468 X-HE-Meta: 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.001643, 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, May 01, 2024 at 02:54:20AM -0700, Breno Leitao wrote: > A memcg pointer in the per-cpu stock can be accessed by drain_all_stock() > and consume_stock() in parallel, causing a potential race. > > KCSAN shows this data-race clearly in the splat below: > > BUG: KCSAN: data-race in drain_all_stock.part.0 / try_charge_memcg > > write to 0xffff88903f8b0788 of 4 bytes by task 35901 on cpu 2: > try_charge_memcg (mm/memcontrol.c:2323 mm/memcontrol.c:2746) > __mem_cgroup_charge (mm/memcontrol.c:7287 mm/memcontrol.c:7301) > do_anonymous_page (mm/memory.c:1054 mm/memory.c:4375 mm/memory.c:4433) > __handle_mm_fault (mm/memory.c:3878 mm/memory.c:5300 mm/memory.c:5441) > handle_mm_fault (mm/memory.c:5606) > do_user_addr_fault (arch/x86/mm/fault.c:1363) > exc_page_fault (./arch/x86/include/asm/irqflags.h:37 > ./arch/x86/include/asm/irqflags.h:72 > arch/x86/mm/fault.c:1513 > arch/x86/mm/fault.c:1563) > asm_exc_page_fault (./arch/x86/include/asm/idtentry.h:623) > > read to 0xffff88903f8b0788 of 4 bytes by task 287 on cpu 27: > drain_all_stock.part.0 (mm/memcontrol.c:2433) > mem_cgroup_css_offline (mm/memcontrol.c:5398 mm/memcontrol.c:5687) > css_killed_work_fn (kernel/cgroup/cgroup.c:5521 kernel/cgroup/cgroup.c:5794) > process_one_work (kernel/workqueue.c:3254) > worker_thread (kernel/workqueue.c:3329 kernel/workqueue.c:3416) > kthread (kernel/kthread.c:388) > ret_from_fork (arch/x86/kernel/process.c:147) > ret_from_fork_asm (arch/x86/entry/entry_64.S:257) > > value changed: 0x00000014 -> 0x00000013 > > This happens because drain_all_stock() is reading stock->nr_pages, while > consume_stock() might be updating the same address, causing a potential > data-race. > > Make the shared addresses bulletproof regarding to reads and writes, > similarly to what stock->cached_objcg and stock->cached. > Annotate all accesses to stock->nr_pages with READ_ONCE()/WRITE_ONCE(). > > Signed-off-by: Breno Leitao Acked-by: Shakeel Butt