From: Andrea Arcangeli <aarcange@redhat.com>
To: Hugh Dickins <hughd@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
Rik van Riel <riel@redhat.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] mm: fix hang on anon_vma->root->lock
Date: Fri, 27 Aug 2010 11:55:46 +0200 [thread overview]
Message-ID: <20100827095546.GC6803@random.random> (raw)
In-Reply-To: <AANLkTimgKcP78CNakDf34NrVrd5apfXrtptNw+G6G5DK@mail.gmail.com>
On Thu, Aug 26, 2010 at 06:43:31PM -0700, Hugh Dickins wrote:
> some light., I think you're mistaking the role that RCU plays here.
That's exactly correct, I thought it prevented reuse of the slab
entry, not only of the whole slab... SLAB_DESTROY_BY_RCU is a lot more
tricky to use than I though...
However at the light of this, I think page_lock_anon_vma could have
returned a freed and reused anon_vma well before the anon-vma changes.
The anon_vma could have been freed after the first page_mapped check
succeed but before taking the spinlock. I think, it worked fine
because the rmap walks are robust enough just not to fall apart on a
reused anon_vma while the lock is hold. It become a visible problem
now because we were unlocking the wrong lock leading to a
deadlock. But I guess it wasn't too intentional to return a reused
anon_vma out of page_lock_anon_vma.
WARNING: multiple messages have this Message-ID (diff)
From: Andrea Arcangeli <aarcange@redhat.com>
To: Hugh Dickins <hughd@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
Rik van Riel <riel@redhat.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] mm: fix hang on anon_vma->root->lock
Date: Fri, 27 Aug 2010 11:55:46 +0200 [thread overview]
Message-ID: <20100827095546.GC6803@random.random> (raw)
In-Reply-To: <AANLkTimgKcP78CNakDf34NrVrd5apfXrtptNw+G6G5DK@mail.gmail.com>
On Thu, Aug 26, 2010 at 06:43:31PM -0700, Hugh Dickins wrote:
> some light., I think you're mistaking the role that RCU plays here.
That's exactly correct, I thought it prevented reuse of the slab
entry, not only of the whole slab... SLAB_DESTROY_BY_RCU is a lot more
tricky to use than I though...
However at the light of this, I think page_lock_anon_vma could have
returned a freed and reused anon_vma well before the anon-vma changes.
The anon_vma could have been freed after the first page_mapped check
succeed but before taking the spinlock. I think, it worked fine
because the rmap walks are robust enough just not to fall apart on a
reused anon_vma while the lock is hold. It become a visible problem
now because we were unlocking the wrong lock leading to a
deadlock. But I guess it wasn't too intentional to return a reused
anon_vma out of page_lock_anon_vma.
--
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next prev parent reply other threads:[~2010-08-27 9:56 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-08-26 6:12 [PATCH] mm: fix hang on anon_vma->root->lock Hugh Dickins
2010-08-26 6:12 ` Hugh Dickins
2010-08-26 6:41 ` David Miller
2010-08-26 6:41 ` David Miller
2010-08-26 10:54 ` Hugh Dickins
2010-08-26 10:54 ` Hugh Dickins
2010-08-26 19:00 ` David Miller
2010-08-26 19:00 ` David Miller
2010-08-27 0:19 ` Andrea Arcangeli
2010-08-27 0:19 ` Andrea Arcangeli
2010-08-26 13:32 ` Rik van Riel
2010-08-26 13:32 ` Rik van Riel
2010-08-26 23:50 ` Andrea Arcangeli
2010-08-26 23:50 ` Andrea Arcangeli
2010-08-27 1:43 ` Hugh Dickins
2010-08-27 1:43 ` Hugh Dickins
2010-08-27 9:55 ` Andrea Arcangeli [this message]
2010-08-27 9:55 ` Andrea Arcangeli
2010-08-27 16:43 ` Hugh Dickins
2010-08-27 16:43 ` Hugh Dickins
2010-08-27 17:13 ` Christoph Lameter
2010-08-27 17:13 ` Christoph Lameter
2010-08-27 17:55 ` Hugh Dickins
2010-08-27 17:55 ` Hugh Dickins
2010-08-27 19:29 ` Christoph Lameter
2010-08-27 19:29 ` Christoph Lameter
2010-08-27 20:14 ` Hugh Dickins
2010-08-27 20:14 ` Hugh Dickins
2010-08-27 20:56 ` Christoph Lameter
2010-08-27 20:56 ` Christoph Lameter
2010-08-27 21:28 ` Hugh Dickins
2010-08-27 21:28 ` Hugh Dickins
2010-08-27 21:33 ` Hugh Dickins
2010-08-27 21:33 ` Hugh Dickins
2010-08-27 23:06 ` Christoph Lameter
2010-08-27 23:06 ` Christoph Lameter
2010-08-28 1:07 ` Hugh Dickins
2010-08-28 1:07 ` Hugh Dickins
2010-08-28 2:47 ` Christoph Lameter
2010-08-28 2:47 ` Christoph Lameter
2010-08-28 10:17 ` Peter Zijlstra
2010-08-28 10:17 ` Peter Zijlstra
2010-08-28 15:54 ` Andrea Arcangeli
2010-08-28 15:54 ` Andrea Arcangeli
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