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Date: Fri, 27 May 2016 11:51:40 -0400
From: Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH] memcg: add RCU locking around
 css_for_each_descendant_pre() in memcg_offline_kmem()
Message-ID: <20160527155140.GN23194@mtj.duckdns.org>
References: <20160526203018.GG23194@mtj.duckdns.org>
 <20160526140202.077d611dbe0926ce290b4e53@linux-foundation.org>
 <20160527153124.GT27686@dhcp22.suse.cz>
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To: Michal Hocko <mhocko@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>, Johannes Weiner <hannes@cmpxchg.org>, Vladimir Davydov <vdavydov@virtuozzo.com>, cgroups@vger.kernel.org, linux-mm@kvack.org, kernel-team@fb.com

On Fri, May 27, 2016 at 05:31:24PM +0200, Michal Hocko wrote:
> On Thu 26-05-16 14:02:02, Andrew Morton wrote:
> > On Thu, 26 May 2016 16:30:18 -0400 Tejun Heo <tj@kernel.org> wrote:
> > 
> > > memcg_offline_kmem() may be called from memcg_free_kmem() after a css
> > > init failure.  memcg_free_kmem() is a ->css_free callback which is
> > > called without cgroup_mutex and memcg_offline_kmem() ends up using
> > > css_for_each_descendant_pre() without any locking.  Fix it by adding
> > > rcu read locking around it.
> > > 
> > >  mkdir: cannot create directory ___65530___: No space left on device
> > >  [  527.241361] ===============================
> > >  [  527.241845] [ INFO: suspicious RCU usage. ]
> > >  [  527.242367] 4.6.0-work+ #321 Not tainted
> > >  [  527.242730] -------------------------------
> > >  [  527.243220] kernel/cgroup.c:4008 cgroup_mutex or RCU read lock required!
> > 
> > cc:stable?
> 
> Also which kernel versions would be affected? I have tried to look and
> got lost in the indirection of the css_free path.

I think it's actually from 0b8f73e10428 ("mm: memcontrol: clean up
alloc, online, offline, free functions") which got merged during this
cycle, so no need for -stable.

Thanks.

-- 
tejun

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From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Subject: Re: [PATCH] memcg: add RCU locking around
 css_for_each_descendant_pre() in memcg_offline_kmem()
Date: Fri, 27 May 2016 11:51:40 -0400
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 <20160527153124.GT27686@dhcp22.suse.cz>
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To: Michal Hocko <mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Cc: Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, Vladimir Davydov <vdavydov-5HdwGun5lf+gSpxsJD1C4w@public.gmane.org>, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, kernel-team-b10kYP2dOMg@public.gmane.org

On Fri, May 27, 2016 at 05:31:24PM +0200, Michal Hocko wrote:
> On Thu 26-05-16 14:02:02, Andrew Morton wrote:
> > On Thu, 26 May 2016 16:30:18 -0400 Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> wrote:
> > 
> > > memcg_offline_kmem() may be called from memcg_free_kmem() after a css
> > > init failure.  memcg_free_kmem() is a ->css_free callback which is
> > > called without cgroup_mutex and memcg_offline_kmem() ends up using
> > > css_for_each_descendant_pre() without any locking.  Fix it by adding
> > > rcu read locking around it.
> > > 
> > >  mkdir: cannot create directory ___65530___: No space left on device
> > >  [  527.241361] ===============================
> > >  [  527.241845] [ INFO: suspicious RCU usage. ]
> > >  [  527.242367] 4.6.0-work+ #321 Not tainted
> > >  [  527.242730] -------------------------------
> > >  [  527.243220] kernel/cgroup.c:4008 cgroup_mutex or RCU read lock required!
> > 
> > cc:stable?
> 
> Also which kernel versions would be affected? I have tried to look and
> got lost in the indirection of the css_free path.

I think it's actually from 0b8f73e10428 ("mm: memcontrol: clean up
alloc, online, offline, free functions") which got merged during this
cycle, so no need for -stable.

Thanks.

-- 
tejun