From: Jens Axboe <axboe@fb.com>
Date: Wed, 12 Feb 2014 16:34:01 +0000 (-0700)
Subject: block: add cond_resched() to potentially long running ioctl discard loop
X-Git-Tag: firefly_0821_release~176^2~4428^2
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=c8123f8c9cb517403b51aa41c3c46ff5e10b2c17;p=firefly-linux-kernel-4.4.55.git

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>
---

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);