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authorVlastimil Babka <vbabka@suse.cz>2014-04-07 15:37:50 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-08-07 12:00:11 -0700
commit21dbd45fb3355f60ac73371e4612a3aa26d07124 (patch)
parent9c98268072b611fab39eee633e3f2e7b2d8c64da (diff)
mm: try_to_unmap_cluster() should lock_page() before mlocking
commit 57e68e9cd65b4b8eb4045a1e0d0746458502554c upstream. A BUG_ON(!PageLocked) was triggered in mlock_vma_page() by Sasha Levin fuzzing with trinity. The call site try_to_unmap_cluster() does not lock the pages other than its check_page parameter (which is already locked). The BUG_ON in mlock_vma_page() is not documented and its purpose is somewhat unclear, but apparently it serializes against page migration, which could otherwise fail to transfer the PG_mlocked flag. This would not be fatal, as the page would be eventually encountered again, but NR_MLOCK accounting would become distorted nevertheless. This patch adds a comment to the BUG_ON in mlock_vma_page() and munlock_vma_page() to that effect. The call site try_to_unmap_cluster() is fixed so that for page != check_page, trylock_page() is attempted (to avoid possible deadlocks as we already have check_page locked) and mlock_vma_page() is performed only upon success. If the page lock cannot be obtained, the page is left without PG_mlocked, which is again not a problem in the whole unevictable memory design. Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Bob Liu <bob.liu@oracle.com> Reported-by: Sasha Levin <sasha.levin@oracle.com> Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com> Cc: Michel Lespinasse <walken@google.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Acked-by: Rik van Riel <riel@redhat.com> Cc: David Rientjes <rientjes@google.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Hugh Dickins <hughd@google.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings <ben@decadent.org.uk> Cc: Yijing Wang <wangyijing@huawei.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2 files changed, 14 insertions, 2 deletions
diff --git a/mm/mlock.c b/mm/mlock.c
index ef726e8aa8e9..7a84dd1f5ec6 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -78,6 +78,7 @@ void __clear_page_mlock(struct page *page)
void mlock_vma_page(struct page *page)
+ /* Serialize with page migration */
if (!TestSetPageMlocked(page)) {
@@ -105,6 +106,7 @@ void mlock_vma_page(struct page *page)
void munlock_vma_page(struct page *page)
+ /* For try_to_munlock() and to serialize with page migration */
if (TestClearPageMlocked(page)) {
diff --git a/mm/rmap.c b/mm/rmap.c
index 6dc46f345dba..695eaff55d77 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1449,9 +1449,19 @@ static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
BUG_ON(!page || PageAnon(page));
if (locked_vma) {
- mlock_vma_page(page); /* no-op if already mlocked */
- if (page == check_page)
+ if (page == check_page) {
+ /* we know we have check_page locked */
+ mlock_vma_page(page);
+ } else if (trylock_page(page)) {
+ /*
+ * If we can lock the page, perform mlock.
+ * Otherwise leave the page alone, it will be
+ * eventually encountered again later.
+ */
+ mlock_vma_page(page);
+ unlock_page(page);
+ }
continue; /* don't unmap */