[3.11.y.z extended stable] Patch "block: add cond_resched() to potentially long running ioctl discard" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

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

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 46d61c4a64caeb15b2ead199eae89af54ee38524 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe at fb.com>
Date: Wed, 12 Feb 2014 09:34:01 -0700
Subject: block: add cond_resched() to potentially long running ioctl discard
 loop

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 at fb.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 block/blk-lib.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/block/blk-lib.c b/block/blk-lib.c
index d6f50d5..9a32f58 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -121,6 +121,14 @@ 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);

--
1.9.0