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[2603:800c:1a02:1bae:e24f:43ff:fee6:449f]) by smtp.gmail.com with ESMTPSA id nk11sm3743647pjb.55.2022.02.01.14.48.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 01 Feb 2022 14:48:42 -0800 (PST) Date: Tue, 1 Feb 2022 12:48:41 -1000 From: Tejun Heo To: Roman Gushchin Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Alexander Egorenkov , Waiman Long , Johannes Weiner , Shakeel Butt , Jeremy Linton , cgroups@vger.kernel.org Subject: Re: [PATCH RESEND] mm: memcg: synchronize objcg lists with a dedicated spinlock Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: B435840006 X-Stat-Signature: aenbb7upetyrkkoi7umsfee4tzk7bgp3 Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=CJBxYQNI; dmarc=fail reason="SPF not aligned (relaxed), DKIM not aligned (relaxed)" header.from=kernel.org (policy=none); spf=pass (imf04.hostedemail.com: domain of htejun@gmail.com designates 209.85.215.181 as permitted sender) smtp.mailfrom=htejun@gmail.com X-Rspam-User: nil X-HE-Tag: 1643755724-933866 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: On Tue, Feb 01, 2022 at 02:33:04PM -0800, Roman Gushchin wrote: ... > In this example a slab allocation from __send_signal() caused a > refilling and draining of a percpu objcg stock, resulted in a > releasing of another non-related objcg. Objcg release path requires > taking the css_set_lock, which is used to synchronize objcg lists. > > This can create a circular dependency with the sighandler lock, > which is taken with the locked css_set_lock by the freezer code > (to freeze a task). > > In general it seems that using css_set_lock to synchronize objcg lists > makes any slab allocations and deallocation with the locked > css_set_lock and any intervened locks risky. > > To fix the problem and make the code more robust let's stop using > css_set_lock to synchronize objcg lists and use a new dedicated > spinlock instead. > > Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API") > Signed-off-by: Roman Gushchin > Reported-by: Alexander Egorenkov > Tested-by: Alexander Egorenkov > Reviewed-by: Waiman Long > Cc: Tejun Heo > Cc: Johannes Weiner > Cc: Shakeel Butt > Cc: Jeremy Linton > Cc: cgroups@vger.kernel.org Acked-by: Tejun Heo I suppose this will go through -mm? If you want me to route it through the cgroup tree, please let me know. Thanks. -- tejun