md: avoid spinlock problem in blk_throtl_exit

blk_throtl_exit assumes that ->queue_lock still exists,
so make sure that it does.
To do this, we stop redirecting ->queue_lock to conf->device_lock
and leave it pointing where it is initialised - __queue_lock.

As the blk_plug functions check the ->queue_lock is held, we now
take that spin_lock explicitly around the plug functions.  We don't
need the locking, just the warning removal.

This is needed for any kernel with the blk_throtl code, which is
which is 2.6.37 and later.

Cc: stable@kernel.org
Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 4 insertions, 3 deletions

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 3b607b28741b..747d061d8e05 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -662,7 +662,10 @@ static int flush_pending_writes(conf_t *conf)
         if (conf->pending_bio_list.head) {
                 struct bio *bio;
                 bio = bio_list_get(&conf->pending_bio_list);
+                /* Spinlock only taken to quiet a warning */
+                spin_lock(conf->mddev->queue->queue_lock);
                 blk_remove_plug(conf->mddev->queue);
+                spin_unlock(conf->mddev->queue->queue_lock);
                 spin_unlock_irq(&conf->device_lock);
                 /* flush any pending bitmap writes to disk
                  * before proceeding w/ I/O */
@@ -971,7 +974,7 @@ static int make_request(mddev_t *mddev, struct bio * bio)
                 atomic_inc(&r10_bio->remaining);
                 spin_lock_irqsave(&conf->device_lock, flags);
                 bio_list_add(&conf->pending_bio_list, mbio);
-                blk_plug_device(mddev->queue);
+                blk_plug_device_unlocked(mddev->queue);
                 spin_unlock_irqrestore(&conf->device_lock, flags);
         }
 
@@ -2304,8 +2307,6 @@ static int run(mddev_t *mddev)
         if (!conf)
                 goto out;
 
-        mddev->queue->queue_lock = &conf->device_lock;
-
         mddev->thread = conf->thread;
         conf->thread = NULL;