From: Andrea Arcangeli <aarcange@redhat.com>
Date: Fri, 28 Sep 2012 12:35:31 +0000 (+0200)
Subject: thp: avoid VM_BUG_ON page_count(page) false positives in __collapse_huge_page_copy
X-Git-Tag: MMI-PSA29.97-13-9~15941
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=99a1300e1d84709f419182bb5189760e78234882;p=GitHub%2FMotorolaMobilityLLC%2Fkernel-slsi.git

thp: avoid VM_BUG_ON page_count(page) false positives in __collapse_huge_page_copy

Speculative cache pagecache lookups can elevate the refcount from
under us, so avoid the false positive. If the refcount is < 2 we'll be
notified by a VM_BUG_ON in put_page_testzero as there are two
put_page(src_page) in a row before returning from this function.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Petr Holasek <pholasek@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 57c4b9309015..141dbb695097 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1811,7 +1811,6 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
 			src_page = pte_page(pteval);
 			copy_user_highpage(page, src_page, address, vma);
 			VM_BUG_ON(page_mapcount(src_page) != 1);
-			VM_BUG_ON(page_count(src_page) != 2);
 			release_pte_page(src_page);
 			/*
 			 * ptl mostly unnecessary, but preempt has to