From: Hugh Dickins <hughd@google.com>
Date: Thu, 26 Aug 2010 06:12:54 +0000 (-0700)
Subject: mm: fix hang on anon_vma->root->lock
X-Git-Tag: v2.6.36-rc3~21
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f18194275c39835cb84563500995e0d503a32d9a;p=pandora-kernel.git

mm: fix hang on anon_vma->root->lock

After several hours, kbuild tests hang with anon_vma_prepare() spinning on
a newly allocated anon_vma's lock - on a box with CONFIG_TREE_PREEMPT_RCU=y
(which makes this very much more likely, but it could happen without).

The ever-subtle page_lock_anon_vma() now needs a further twist: since
anon_vma_prepare() and anon_vma_fork() are liable to change the ->root
of a reused anon_vma structure at any moment, page_lock_anon_vma()
needs to check page_mapped() again before succeeding, otherwise
page_unlock_anon_vma() might address a different root->lock.

Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

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