[3.8.y.z extended stable] Patch "dm delay: fix a possible deadlock due to shared workqueue" has been added to staging queue

[Kamal Mostafa]

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

    dm delay: fix a possible deadlock due to shared workqueue

to the linux-3.8.y-queue branch of the 3.8.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-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.16.

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

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From da3b6ca4de408a92101fe84f0bf82ea0fbf6baed Mon Sep 17 00:00:00 2001
From: Mikulas Patocka <mpatocka at redhat.com>
Date: Fri, 15 Nov 2013 16:12:20 -0500
Subject: dm delay: fix a possible deadlock due to shared workqueue

commit 718822c1c112dc99e0c72c8968ee1db9d9d910f0 upstream.

The dm-delay target uses a shared workqueue for multiple instances.  This
can cause deadlock if two or more dm-delay targets are stacked on the top
of each other.

This patch changes dm-delay to use a per-instance workqueue.

Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>
Signed-off-by: Mike Snitzer <snitzer at redhat.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/md/dm-delay.c | 23 +++++++++++------------
 1 file changed, 11 insertions(+), 12 deletions(-)

diff --git a/drivers/md/dm-delay.c b/drivers/md/dm-delay.c
index c0d03b0..7c4c725 100644
--- a/drivers/md/dm-delay.c
+++ b/drivers/md/dm-delay.c
@@ -20,6 +20,7 @@
 struct delay_c {
 	struct timer_list delay_timer;
 	struct mutex timer_lock;
+	struct workqueue_struct *kdelayd_wq;
 	struct work_struct flush_expired_bios;
 	struct list_head delayed_bios;
 	atomic_t may_delay;
@@ -45,14 +46,13 @@ struct dm_delay_info {

 static DEFINE_MUTEX(delayed_bios_lock);

-static struct workqueue_struct *kdelayd_wq;
 static struct kmem_cache *delayed_cache;

 static void handle_delayed_timer(unsigned long data)
 {
 	struct delay_c *dc = (struct delay_c *)data;

-	queue_work(kdelayd_wq, &dc->flush_expired_bios);
+	queue_work(dc->kdelayd_wq, &dc->flush_expired_bios);
 }

 static void queue_timeout(struct delay_c *dc, unsigned long expires)
@@ -191,6 +191,12 @@ out:
 		goto bad_dev_write;
 	}

+	dc->kdelayd_wq = alloc_workqueue("kdelayd", WQ_MEM_RECLAIM, 0);
+	if (!dc->kdelayd_wq) {
+		DMERR("Couldn't start kdelayd");
+		goto bad_queue;
+	}
+
 	setup_timer(&dc->delay_timer, handle_delayed_timer, (unsigned long)dc);

 	INIT_WORK(&dc->flush_expired_bios, flush_expired_bios);
@@ -203,6 +209,8 @@ out:
 	ti->private = dc;
 	return 0;

+bad_queue:
+	mempool_destroy(dc->delayed_pool);
 bad_dev_write:
 	if (dc->dev_write)
 		dm_put_device(ti, dc->dev_write);
@@ -217,7 +225,7 @@ static void delay_dtr(struct dm_target *ti)
 {
 	struct delay_c *dc = ti->private;

-	flush_workqueue(kdelayd_wq);
+	destroy_workqueue(dc->kdelayd_wq);

 	dm_put_device(ti, dc->dev_read);

@@ -350,12 +358,6 @@ static int __init dm_delay_init(void)
 {
 	int r = -ENOMEM;

-	kdelayd_wq = alloc_workqueue("kdelayd", WQ_MEM_RECLAIM, 0);
-	if (!kdelayd_wq) {
-		DMERR("Couldn't start kdelayd");
-		goto bad_queue;
-	}
-
 	delayed_cache = KMEM_CACHE(dm_delay_info, 0);
 	if (!delayed_cache) {
 		DMERR("Couldn't create delayed bio cache.");
@@ -373,8 +375,6 @@ static int __init dm_delay_init(void)
 bad_register:
 	kmem_cache_destroy(delayed_cache);
 bad_memcache:
-	destroy_workqueue(kdelayd_wq);
-bad_queue:
 	return r;
 }

@@ -382,7 +382,6 @@ static void __exit dm_delay_exit(void)
 {
 	dm_unregister_target(&delay_target);
 	kmem_cache_destroy(delayed_cache);
-	destroy_workqueue(kdelayd_wq);
 }

 /* Module hooks */
--
1.8.3.2