From 0f79960391a5a1e3679956024e18aeeb0369ac44 Mon Sep 17 00:00:00 2001 From: Mike Snitzer Date: Wed, 6 Jul 2011 21:30:50 +0200 Subject: block: eliminate potential for infinite loop in blkdev_issue_discard Due to the recently identified overflow in read_capacity_16() it was possible for max_discard_sectors to be zero but still have discards enabled on the associated device's queue. Eliminate the possibility for blkdev_issue_discard to infinitely loop. Interestingly this issue wasn't identified until a device, whose discard_granularity was 0 due to read_capacity_16 overflow, was consumed by blk_stack_limits() to construct limits for a higher-level DM multipath device. The multipath device's resulting limits never had the discard limits stacked because blk_stack_limits() will only do so if the bottom device's discard_granularity != 0. This resulted in the multipath device's limits.max_discard_sectors being 0. Signed-off-by: Mike Snitzer Signed-off-by: Jens Axboe --- block/blk-lib.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) (limited to 'block') diff --git a/block/blk-lib.c b/block/blk-lib.c index 78e627e2581d..64974b1c7cca 100644 --- a/block/blk-lib.c +++ b/block/blk-lib.c @@ -59,7 +59,10 @@ 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. Being cautious never hurts. */ + return -EOPNOTSUPP; + } else if (q->limits.discard_granularity) { unsigned int disc_sects = q->limits.discard_granularity >> 9; max_discard_sectors &= ~(disc_sects - 1); -- cgit v1.2.3