[SCSI] bsg: fix bsg_mutex hang with device removal

We don't need to hold bsg_mutex during bsg_complete_all_commands(). It
leads to a problem that we block bsg_unregister_queue during
bsg_complete_all_commands (untill all the outstanding commands
complete).

Thanks to Pete Wyckoff for finding the bug and testing the patch.

The detailed bug report is:

http://marc.info/?l=linux-scsi&m=121182137132145&w=2

Tested-by: Pete Wyckoff <pw@osc.edu>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

block/bsg.c

@@ -724,8 +724,13 @@ static int bsg_put_device(struct bsg_device *bd)
 	mutex_lock(&bsg_mutex);
 
 	do_free = atomic_dec_and_test(&bd->ref_count);
-	if (!do_free)
+	if (!do_free) {
+		mutex_unlock(&bsg_mutex);
 		goto out;
+	}
+
+	hlist_del(&bd->dev_list);
+	mutex_unlock(&bsg_mutex);
 
 	dprintk("%s: tearing down\n", bd->name);
 
@@ -741,10 +746,8 @@ static int bsg_put_device(struct bsg_device *bd)
 	 */
 	ret = bsg_complete_all_commands(bd);
 
-	hlist_del(&bd->dev_list);
 	kfree(bd);
 out:
-	mutex_unlock(&bsg_mutex);
 	kref_put(&q->bsg_dev.ref, bsg_kref_release_function);
 	if (do_free)
 		blk_put_queue(q);