blk-mq: fix deadlock in blk_mq_register_disk() error path

If we fail registering any of the hardware queues, we call
into blk_mq_unregister_disk() with the hotplug mutex already
held. Since blk_mq_unregister_disk() attempts to acquire the
same mutex, we end up in a less than happy place.

Reported-by: Jinpu Wang <jinpu.wang@profitbricks.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
index 4ea4dd8..fe822aa 100644 (file)
--- a/block/blk-mq-sysfs.c
+++ b/block/blk-mq-sysfs.c
@@ -380,15 +380,13 @@ static int blk_mq_register_hctx(struct blk_mq_hw_ctx *hctx)
        return ret;
 }
 
-void blk_mq_unregister_disk(struct gendisk *disk)
+static void __blk_mq_unregister_disk(struct gendisk *disk)
 {
        struct request_queue *q = disk->queue;
        struct blk_mq_hw_ctx *hctx;
        struct blk_mq_ctx *ctx;
        int i, j;
 
-       blk_mq_disable_hotplug();
-
        queue_for_each_hw_ctx(q, hctx, i) {
                blk_mq_unregister_hctx(hctx);
 
@@ -405,6 +403,12 @@ void blk_mq_unregister_disk(struct gendisk *disk)
        kobject_put(&disk_to_dev(disk)->kobj);
 
        q->mq_sysfs_init_done = false;
+}
+
+void blk_mq_unregister_disk(struct gendisk *disk)
+{
+       blk_mq_disable_hotplug();
+       __blk_mq_unregister_disk(disk);
        blk_mq_enable_hotplug();
 }
 
@@ -450,7 +454,7 @@ int blk_mq_register_disk(struct gendisk *disk)
        }
 
        if (ret)
-               blk_mq_unregister_disk(disk);
+               __blk_mq_unregister_disk(disk);
        else
                q->mq_sysfs_init_done = true;
 out: