[PATCH 3.2 107/200] block: add cond_resched() to potentially long running ioctl discard loop

From: Ben Hutchings
Date: Sun Mar 30 2014 - 19:58:44 EST

3.2.56-rc1 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

Signed-off-by: Jens Axboe <axboe@xxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
block/blk-lib.c | 8 ++++++++
1 file changed, 8 insertions(+)

--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -101,6 +101,14 @@ int blkdev_issue_discard(struct block_de

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 */

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