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[2a03:2880:30ff:74::face:b00c]) by smtp.gmail.com with ESMTPSA id xa8-20020a170907b9c800b00a59eb443e01sm922487ejc.74.2024.05.07.09.03.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 07 May 2024 09:03:02 -0700 (PDT) Date: Tue, 7 May 2024 09:03:00 -0700 From: Breno Leitao To: Michal Hocko Cc: Johannes Weiner , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , leit@meta.com, "open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" , "open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" , open list Subject: Re: [PATCH] memcg: Fix data-race KCSAN bug in rstats Message-ID: References: <20240424125940.2410718-1-leitao@debian.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: D0324180024 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: kqhxk1yncc7ez6pq6hn8ag56suue37pg X-HE-Tag: 1715097784-864768 X-HE-Meta: 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 Cv7iHHBw rH6TYTJ1TFGfJHUH7+xxmdVEagxyXTFSMfdAMfBFrDe/ODyCtRf4lKQUvN4MlreCl2nvjLff4bnCrODoq6CO652vMbZYMCPiYBdvsjO8Feh1rPXwOqOI2hLWCi+uEVGeQuHJcCCAMTFTnSLwEcoeRYXeWjT7gnLxxiSClJlrFCx2sZ69HV1k+hvSVZ7sfZV3l13l2JKyK10BebVBf3znoxKkA1C0GsmNEwWB16qnzA6OXUUjeCvj5hPoqgaA5Grnafci9Ew6z9XfEDicgGy9Mh6Yzle+pIlQYHI7LmXv7htWT3+6weNmHBgXGGPz0xHnm/u2ZnIvzOeZj5DhTBHzd0jwIXSFyjOYuAYrzNBcj270kAwvNlsTjbXXFnJJKUnWd0x3EFdHsHyWfOEY= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000018, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hello Michal, On Fri, May 03, 2024 at 01:27:41PM +0200, Michal Hocko wrote: > On Wed 24-04-24 05:59:39, Breno Leitao wrote: > > 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. > > It is worth mentioning that the race is harmless. Are you suggesting that the race consistently avoids producing corrupt data, or even if corruption occurs, it's inconsequential because it only affects statistics? If there's no data corruption, does it incur any performance drawbacks? Thanks!