staging: android: ashmem: Shrink directly through shmem_fallocate

When ashmem_shrink is called from direct reclaim on a user thread, a
call to do_fallocate will check for permissions against the security
policy of that user thread.  It can thus fail by chance if called on a
thread that isn't permitted to modify the relevant ashmem areas.

Because we know that we have a shmem file underneath, call the shmem
implementation of fallocate directly instead of going through the
user-space interface for fallocate.
Signed-off-by: Tobias Lindskog <tobias.lindskog@sonymobile.com>
Signed-off-by: Jeff Vander Stoep <jeffv@google.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/android/ashmem.c

@@ -450,9 +450,9 @@ ashmem_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
 		loff_t start = range->pgstart * PAGE_SIZE;
 		loff_t end = (range->pgend + 1) * PAGE_SIZE;
 
-		vfs_fallocate(range->asma->file,
-			      FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
-			      start, end - start);
+		range->asma->file->f_op->fallocate(range->asma->file,
+				FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
+				start, end - start);
 		range->purged = ASHMEM_WAS_PURGED;
 		lru_del(range);