linux-kernel - [PATCH 3.12 66/82] block: add cond_resched() to potentially long running ioctl discard loop

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Message-Id: <20140220235021.459282592@linuxfoundation.org>
Date:	Thu, 20 Feb 2014 15:52:49 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Jens Axboe <axboe@...com>
Subject: [PATCH 3.12 66/82] block: add cond_resched() to potentially long running ioctl discard loop

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

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

From: Jens Axboe <axboe@...com>

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@...com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 block/blk-lib.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -121,6 +121,14 @@ int blkdev_issue_discard(struct block_de
 
 		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);
 


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