Eric Lee / smarc-ti-linux-kernel

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Commit 57e68e9cd65b4b8eb4045a1e0d0746458502554c

Authored by Vlastimil Babka
Committed by Linus Torvalds
1 parent 3a025760fc
Exists in master and in 13 other branches dlt-processor-sdk-linux-03.00.00.04, processor-sdk-linux-02.00.01, smarc-ti-linux-3.15.y, smarc-ti-lsk-linux-4.1.y, smarct3x-processor-sdk-04.01.00.06, smarct3x-processor-sdk-linux-02.00.01, smarct3x-processor-sdk-linux-03.00.00.04, smarct4x-800-processor-sdk-linux-02.00.01, smarct4x-processor-sdk-04.01.00.06, smarct4x-processor-sdk-linux-02.00.01, smarct4x-processor-sdk-linux-03.00.00.04, ti-linux-3.15.y, ti-lsk-linux-4.1.y

mm: try_to_unmap_cluster() should lock_page() before mlocking 

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>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Showing 2 changed files with 14 additions and 2 deletions Side-by-side Diff

... ... @@ -79,6 +79,7 @@
79 79 */
80 80 void mlock_vma_page(struct page *page)
81 81 {
  82 + /* Serialize with page migration */
82 83 BUG_ON(!PageLocked(page));
83 84  
84 85 if (!TestSetPageMlocked(page)) {
... ... @@ -174,6 +175,7 @@
174 175 unsigned int nr_pages;
175 176 struct zone *zone = page_zone(page);
176 177  
  178 + /* For try_to_munlock() and to serialize with page migration */
177 179 BUG_ON(!PageLocked(page));
178 180  
179 181 /*
... ... @@ -1332,9 +1332,19 @@
1332 1332 BUG_ON(!page || PageAnon(page));
1333 1333  
1334 1334 if (locked_vma) {
1335   - mlock_vma_page(page); /* no-op if already mlocked */
1336   - if (page == check_page)
  1335 + if (page == check_page) {
  1336 + /* we know we have check_page locked */
  1337 + mlock_vma_page(page);
1337 1338 ret = SWAP_MLOCK;
  1339 + } else if (trylock_page(page)) {
  1340 + /*
  1341 + * If we can lock the page, perform mlock.
  1342 + * Otherwise leave the page alone, it will be
  1343 + * eventually encountered again later.
  1344 + */
  1345 + mlock_vma_page(page);
  1346 + unlock_page(page);
  1347 + }
1338 1348 continue; /* don't unmap */
1339 1349 }
1340 1350