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From: Hugh Dickins <hughd@google.com>
To: Xishi Qiu <qiuxishi@huawei.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Tejun Heo <tj@kernel.org>, Michal Hocko <mhocko@kernel.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Mel Gorman <mgorman@techsingularity.net>,
	Michal Hocko <mhocko@suse.com>, Vlastimil Babka <vbabka@suse.cz>,
	Minchan Kim <minchan@kernel.org>,
	David Rientjes <rientjes@google.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	aarcange@redhat.com, sumeet.keswani@hpe.com,
	Rik van Riel <riel@redhat.com>, Hugh Dickins <hughd@google.com>,
	Linux MM <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	zhong jiang <zhongjiang@huawei.com>
Subject: Re: mm, something wring in page_lock_anon_vma_read()?
Date: Fri, 19 May 2017 15:00:10 -0700 (PDT)	[thread overview]
Message-ID: <alpine.LSU.2.11.1705191453040.3819@eggly.anvils> (raw)
In-Reply-To: <591EBE71.7080402@huawei.com>

On Fri, 19 May 2017, Xishi Qiu wrote:
> On 2017/5/19 16:52, Xishi Qiu wrote:
> > On 2017/5/18 17:46, Xishi Qiu wrote:
> > 
> >> Hi, my system triggers this bug, and the vmcore shows the anon_vma seems be freed.
> >> The kernel is RHEL 7.2, and the bug is hard to reproduce, so I don't know if it
> >> exists in mainline, any reply is welcome!
> >>
> > 
> > When we alloc anon_vma, we will init the value of anon_vma->root,
> > so can we set anon_vma->root to NULL when calling
> > anon_vma_free -> kmem_cache_free(anon_vma_cachep, anon_vma);
> > 
> > anon_vma_free()
> > 	...
> > 	anon_vma->root = NULL;
> > 	kmem_cache_free(anon_vma_cachep, anon_vma);
> > 
> > I find if we do this above, system boot failed, why?
> > 
> 
> If anon_vma was freed, we should not to access the root_anon_vma, because it maybe also
> freed(e.g. anon_vma == root_anon_vma), right?
> 
> page_lock_anon_vma_read()
> 	...
> 	anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
> 	root_anon_vma = ACCESS_ONCE(anon_vma->root);
> 	if (down_read_trylock(&root_anon_vma->rwsem)) {  // it's not safe
> 	...
> 	if (!atomic_inc_not_zero(&anon_vma->refcount)) {  // check anon_vma was not freed
> 	...
> 	anon_vma_lock_read(anon_vma);  // it's safe
> 	...

You're ignoring the rcu_read_lock() on entry to page_lock_anon_vma_read(),
and the SLAB_DESTROY_BY_RCU (recently renamed SLAB_TYPESAFE_BY_RCU) nature
of the anon_vma_cachep kmem cache.  It is not safe to muck with anon_vma->
root in anon_vma_free(), others could still be looking at it.

Hugh

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  reply	other threads:[~2017-05-19 22:00 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-05-18  9:46 mm, something wring in page_lock_anon_vma_read()? Xishi Qiu
2017-05-19  8:52 ` Xishi Qiu
2017-05-19  9:44   ` Xishi Qiu
2017-05-19 22:00     ` Hugh Dickins [this message]
2017-05-20  1:21       ` Xishi Qiu
2017-05-20  2:02         ` Hugh Dickins
2017-05-20  2:18           ` Xishi Qiu
2017-05-20  2:40             ` Hugh Dickins
2017-05-20  3:01               ` zhong jiang
2017-05-22 16:51                 ` Vlastimil Babka
2017-05-23  9:21                   ` zhong jiang
2017-05-23  9:33                     ` Vlastimil Babka
2017-05-23 10:32                       ` zhong jiang
2017-06-08 13:44                       ` Xishi Qiu
2017-06-08 13:59                         ` Vlastimil Babka
2017-06-08 14:11                           ` zhong jiang
2017-07-18 10:59                           ` mm, something wrong " Xishi Qiu
2017-07-19  8:40                             ` Vlastimil Babka
2017-07-19  9:59                               ` Xishi Qiu
2017-07-20 12:58                                 ` Andrea Arcangeli
2017-07-20 16:15                                   ` Andrea Arcangeli
2017-05-22  9:48               ` mm, something wring " Xishi Qiu
2017-05-22 19:26                 ` Hugh Dickins
2017-05-23  2:19                   ` Xishi Qiu
2017-05-23  2:51                     ` Hugh Dickins

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