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From: Roman Gushchin To: Breno Leitao Cc: Johannes Weiner , Michal Hocko , Shakeel Butt , 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: 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: 8AD4E4000D X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: 3pibx43gsgbbpi1gwiykfaoyhkjduf5j X-HE-Tag: 1714605544-765880 X-HE-Meta: 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 S+EgiGTN mzoWoMhC6Vz4zZWc/kS7HKyLkMxq86e81GgKiuunaWlV3tzNNx1TcjZUWu8j2J250EMyG7XynPGDjm4aGDVBsPr+7/s+Ky2IIMA0xnbaSbWTfBHSh/jftE/57+sri1CI6fJuUDba2i1p8U4GicD+7dnAhbwXRDggVO7iaTjTXdWEAyqmQMIRk2xJ3DKuW2d++KuMFSQ28H8FiNlU3eL/HtZBkFw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000010, 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. Btw there is an actual data race, which is periodically causing a needless draining of a per-cpu stock. > > 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 Reviewed-by: Roman Gushchin