block: add cond_resched() to potentially long running ioctl discard loop

When mkfs issues a full device discard and the device only
supports discards of a smallish size, we can loop in
blkdev_issue_discard() for a long time. If preempt isn't enabled,
this can turn into a softlock situation and the kernel will
start complaining.

Add an explicit cond_resched() at the end of the loop to avoid
that.

Cc: stable@kernel.org
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/block/blk-lib.c b/block/blk-lib.c
index 2da76c999ef3..97a733cf3d5f 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -119,6 +119,14 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
 
                 atomic_inc(&bb.done);
                 submit_bio(type, bio);
+
+                /*
+                 * We can loop for a long time in here, if someone does
+                 * full device discards (like mkfs). Be nice and allow
+                 * us to schedule out to avoid softlocking if preempt
+                 * is disabled.
+                 */
+                cond_resched();
         }
         blk_finish_plug(&plug);