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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next prev parent 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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