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@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/md/dm-delay.c b/drivers/md/dm-delay.c
index 11431ac..3f123f1 100644 (file)
--- 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)
@@ -190,6 +190,12 @@ 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);
@@ -202,6 +208,8 @@ 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);
@@ -216,7 +224,7 @@ 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 */