block: eliminate potential for infinite loop in blkdev_issue_discard

Commit Message

Mike Snitzer Sept. 27, 2010, 6:13 p.m. UTC

None

Patch

diff --git a/block/blk-lib.c b/block/blk-lib.c
index c392029..186f249 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -56,7 +56,10 @@  int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
 	 * granularity
 	 */
 	max_discard_sectors = min(q->limits.max_discard_sectors, UINT_MAX >> 9);
-	if (q->limits.discard_granularity) {
+	if (unlikely(!max_discard_sectors)) {
+		/* Avoid infinite loop (below) */
+		return -EOPNOTSUPP;
+	} else if (q->limits.discard_granularity) {
 		unsigned int disc_sects = q->limits.discard_granularity >> 9;
 
 		max_discard_sectors &= ~(disc_sects - 1);