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[209.85.220.65]) by mx.google.com with SMTPS id n202sor4566882qka.66.2019.06.05.06.26.11 for (Google Transport Security); Wed, 05 Jun 2019 06:26:11 -0700 (PDT) Received-SPF: pass (google.com: domain of htejun@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b="k8/Yhbuf"; spf=pass (google.com: domain of htejun@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=htejun@gmail.com; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=s6/pRA/FRv79XWIPs0xt9Lyo0lf431cIWjT6TfF1xds=; b=k8/Yhbufqh3DMYmLycwsD4rntibzmwGLFA8f3BJkBHYziNLbAiTWTtNHG8P/LZXG01 RQr3TuUc7en2wLHZVCPQyU8oTGqg0hN3O3VhWzUdlsZgq7nvJBBc1wHtWnsIISh87nJl tS4mJTrZk63Xn57xRtEf92yZctuaIVJ9RbJRB40XHVYqSOUn5EPxrnw+KvvV+eojCNNs 26TIF/qMy/wLikOWhz0zJ0Z6oQe57wex1ly57qgu8408/ZLDG/a9ZMHgEhxIVSzHjg5G Ah3XhcGeFc/9gT1+wfPOSFQXBxqU9Lm38xTZvkjCj1L7OEGQRoec2kC1w/+rf8Qg82FY b2QQ== X-Google-Smtp-Source: APXvYqyn/0YrgqYDxI+pyotnafRB07J91NtPSDC/hCalcKirkzsBwvMmzeYdvlDQDwYgHNmcrRVsuw== X-Received: by 2002:a37:50d4:: with SMTP id e203mr31499108qkb.83.1559741171252; Wed, 05 Jun 2019 06:26:11 -0700 (PDT) Received: from localhost ([2620:10d:c091:500::1:c027]) by smtp.gmail.com with ESMTPSA id o8sm7701628qtq.18.2019.06.05.06.26.10 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 05 Jun 2019 06:26:10 -0700 (PDT) Date: Wed, 5 Jun 2019 06:26:07 -0700 From: Tejun Heo To: Michal Hocko Cc: Johannes Weiner , Vladimir Davydov , cgroups@vger.kernel.org, linux-mm@kvack.org, kernel-team@fb.com Subject: Re: [PATCH for-5.2-fixes] memcg: Don't loop on css_tryget_online() failure Message-ID: <20190605132607.GI374014@devbig004.ftw2.facebook.com> References: <20190529210617.GP374014@devbig004.ftw2.facebook.com> <20190605125520.GF15685@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190605125520.GF15685@dhcp22.suse.cz> User-Agent: Mutt/1.5.21 (2010-09-15) 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 Wed, Jun 05, 2019 at 02:55:20PM +0200, Michal Hocko wrote: > On Wed 29-05-19 14:06:17, Tejun Heo wrote: > > A PF_EXITING task may stay associated with an offline css. > > get_mem_cgroup_from_mm() may deadlock if mm->owner is in such state. > > All similar logics in memcg are falling back to root memcg on > > tryget_online failure and get_mem_cgroup_from_mm() can do the same. > > > > A similar failure existed for task_get_css() and could be triggered > > through BSD process accounting racing against memcg offlining. See > > 18fa84a2db0e ("cgroup: Use css_tryget() instead of css_tryget_online() > > in task_get_css()") for details. > > > > Signed-off-by: Tejun Heo > > Do we need to mark this patch for stable or this is too unlikely to > happen? This one's a lot less likely than the one in task_get_css() which already is pretty low frequency. I don't think it warrants -stable tagging. Thanks. -- tejun