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From: Johannes Weiner <hannes@cmpxchg.org>
To: Michal Hocko <mhocko@kernel.org>
Cc: Stable tree <stable@vger.kernel.org>,
	Vladimir Davydov <vdavydov@parallels.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
	Nikolay Borisov <kernel@kyup.com>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH stable-4.4 1/3] mm: memcontrol: fix cgroup creation failure after many small jobs
Date: Mon, 15 Aug 2016 09:37:48 -0400	[thread overview]
Message-ID: <20160815133748.GA3775@cmpxchg.org> (raw)
In-Reply-To: <20160815124615.GD3360@dhcp22.suse.cz>

On Mon, Aug 15, 2016 at 02:46:19PM +0200, Michal Hocko wrote:
> On Mon 15-08-16 08:34:07, Johannes Weiner wrote:
> > Hi Michal, thanks for doing this. There is only one issue I can see:
> > 
> > On Fri, Aug 12, 2016 at 11:56:17AM +0200, Michal Hocko wrote:
> > > @@ -4171,17 +4211,27 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
> > >  	if (!memcg)
> > >  		return NULL;
> > >  
> > > +	memcg->id.id = idr_alloc(&mem_cgroup_idr, NULL,
> > > +				 1, MEM_CGROUP_ID_MAX,
> > > +				 GFP_KERNEL);
> > > +	if (memcg->id.id < 0)
> > > +		goto out_free;
> > > +
> > >  	memcg->stat = alloc_percpu(struct mem_cgroup_stat_cpu);
> > >  	if (!memcg->stat)
> > > -		goto out_free;
> > > +		goto out_idr;
> > >  
> > >  	if (memcg_wb_domain_init(memcg, GFP_KERNEL))
> > >  		goto out_free_stat;
> > >  
> > > +	idr_replace(&mem_cgroup_idr, memcg, memcg->id.id);
> > 
> > This publishes the memcg object too early. Before 4.5, the memcg is
> > not fully initialized in mem_cgroup_alloc(). You have to move the
> > idr_replace() down to that function (and idr_remove() on free_out).
> 
> You are right. I am just wondering whether it matters. Nobody should see
> the id so nobody will be looking it up, no?

Page cache shadow entries refer to these IDs weakly. It's possible to
refault with a recently recycled memcg ID and crash. That's why we do
the whole alloc(NULL) -> replace(memcg) dance in the first place.

WARNING: multiple messages have this Message-ID (diff)
From: Johannes Weiner <hannes@cmpxchg.org>
To: Michal Hocko <mhocko@kernel.org>
Cc: Stable tree <stable@vger.kernel.org>,
	Vladimir Davydov <vdavydov@parallels.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
	Nikolay Borisov <kernel@kyup.com>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH stable-4.4 1/3] mm: memcontrol: fix cgroup creation failure after many small jobs
Date: Mon, 15 Aug 2016 09:37:48 -0400	[thread overview]
Message-ID: <20160815133748.GA3775@cmpxchg.org> (raw)
In-Reply-To: <20160815124615.GD3360@dhcp22.suse.cz>

On Mon, Aug 15, 2016 at 02:46:19PM +0200, Michal Hocko wrote:
> On Mon 15-08-16 08:34:07, Johannes Weiner wrote:
> > Hi Michal, thanks for doing this. There is only one issue I can see:
> > 
> > On Fri, Aug 12, 2016 at 11:56:17AM +0200, Michal Hocko wrote:
> > > @@ -4171,17 +4211,27 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
> > >  	if (!memcg)
> > >  		return NULL;
> > >  
> > > +	memcg->id.id = idr_alloc(&mem_cgroup_idr, NULL,
> > > +				 1, MEM_CGROUP_ID_MAX,
> > > +				 GFP_KERNEL);
> > > +	if (memcg->id.id < 0)
> > > +		goto out_free;
> > > +
> > >  	memcg->stat = alloc_percpu(struct mem_cgroup_stat_cpu);
> > >  	if (!memcg->stat)
> > > -		goto out_free;
> > > +		goto out_idr;
> > >  
> > >  	if (memcg_wb_domain_init(memcg, GFP_KERNEL))
> > >  		goto out_free_stat;
> > >  
> > > +	idr_replace(&mem_cgroup_idr, memcg, memcg->id.id);
> > 
> > This publishes the memcg object too early. Before 4.5, the memcg is
> > not fully initialized in mem_cgroup_alloc(). You have to move the
> > idr_replace() down to that function (and idr_remove() on free_out).
> 
> You are right. I am just wondering whether it matters. Nobody should see
> the id so nobody will be looking it up, no?

Page cache shadow entries refer to these IDs weakly. It's possible to
refault with a recently recycled memcg ID and crash. That's why we do
the whole alloc(NULL) -> replace(memcg) dance in the first place.

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  reply	other threads:[~2016-08-15 13:41 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-08-12  9:56 [PATCH stable-4.4 0/3] backport memcg id patches Michal Hocko
2016-08-12  9:56 ` Michal Hocko
2016-08-12  9:56 ` Michal Hocko
2016-08-12  9:56 ` [PATCH stable-4.4 1/3] mm: memcontrol: fix cgroup creation failure after many small jobs Michal Hocko
2016-08-12  9:56   ` Michal Hocko
2016-08-12  9:56   ` Michal Hocko
2016-08-15 12:34   ` Johannes Weiner
2016-08-15 12:34     ` Johannes Weiner
2016-08-15 12:46     ` Michal Hocko
2016-08-15 12:46       ` Michal Hocko
2016-08-15 13:37       ` Johannes Weiner [this message]
2016-08-15 13:37         ` Johannes Weiner
2016-08-15 14:04         ` Michal Hocko
2016-08-15 14:04           ` Michal Hocko
2016-08-15 14:34           ` Johannes Weiner
2016-08-15 14:34             ` Johannes Weiner
2016-08-12  9:56 ` [PATCH stable-4.4 2/3] mm: memcontrol: fix swap counter leak on swapout from offline cgroup Michal Hocko
2016-08-12  9:56   ` Michal Hocko
2016-08-12  9:56   ` Michal Hocko
2016-08-12  9:56 ` [PATCH stable-4.4 3/3] mm: memcontrol: fix memcg id ref counter on swap charge move Michal Hocko
2016-08-12  9:56   ` Michal Hocko
2016-08-12  9:56   ` Michal Hocko
2016-08-14 16:08 ` [PATCH stable-4.4 0/3] backport memcg id patches Greg KH
2016-08-14 16:08   ` Greg KH
2016-08-15 15:06 [PATCH stable-4.4 0/3 v2] " Michal Hocko
2016-08-15 15:06 ` [PATCH stable-4.4 1/3] mm: memcontrol: fix cgroup creation failure after many small jobs Michal Hocko
2016-08-15 15:06   ` Michal Hocko
2016-08-15 15:06   ` Michal Hocko
2016-08-15 15:16   ` Johannes Weiner
2016-08-15 15:16     ` Johannes Weiner
2016-08-15 15:29     ` Michal Hocko
2016-08-15 15:29       ` Michal Hocko
2016-08-15 15:22   ` Greg KH
2016-08-15 15:22     ` Greg KH
2016-08-15 15:33     ` Michal Hocko
2016-08-15 15:33       ` Michal Hocko
2016-08-15 15:35   ` Michal Hocko
2016-08-15 15:35     ` Michal Hocko
2016-08-15 15:35     ` Michal Hocko
2016-08-15 19:09     ` Greg KH
2016-08-15 19:09       ` Greg KH

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