hugetlb: detect race upon page allocation failure during COW
authorHillf Danton <dhillf@gmail.com>
Tue, 10 Jan 2012 23:07:20 +0000 (15:07 -0800)
committerLinus Torvalds <torvalds@linux-foundation.org>
Wed, 11 Jan 2012 00:30:42 +0000 (16:30 -0800)
commita734bcc812146cfba530e1adaf609fce1357982e
tree021fb4187985de65744a3f8f831a5f07130f2e2e
parent5f8aefd44e64ed2f6950a1dcc77309b7dd9979f4
hugetlb: detect race upon page allocation failure during COW

Currently we are not rechecking pte_same in hugetlb_cow after we take ptl
lock again in the page allocation failure code path and simply retry
again.  This is not an issue at the moment because hugetlb fault path is
protected by hugetlb_instantiation_mutex so we cannot race.

The original page is locked and so we cannot race even with the page
migration.

Let's add the pte_same check anyway as we want to be consistent with the
other check later in this function and be safe if we ever remove the
mutex.

[mhocko@suse.cz: reworded the changelog]
Signed-off-by: Hillf Danton <dhillf@gmail.com>
Signed-off-by: Michal Hocko <mhocko@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <jweiner@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/hugetlb.c