[PATCH 3.5 60/60] block: add cond_resched() to potentially long running ioctl discard loop

[Luis Henriques]

3.5.7.31 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jens Axboe <axboe@xxxxxx>

commit c8123f8c9cb517403b51aa41c3c46ff5e10b2c17 upstream.

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.

Signed-off-by: Jens Axboe <axboe@xxxxxx>
[ luis: backported to 3.5: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
 block/blk-lib.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/block/blk-lib.c b/block/blk-lib.c
index 2b461b4..36751e2 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -101,6 +101,14 @@ 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();
 	}
 
 	/* Wait for bios in-flight */
-- 
1.9.0

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