block: release disk reference in hd_struct_free_work

Commit e8c7d14ac6c3 ("block: revert back to synchronous request_queue removal")
stops to release request queue from wq context because that commit
supposed all blk_put_queue() is called in context which is allowed
to sleep. However, this assumption isn't true because we release disk's
reference in partition's percpu_ref's ->release() which doesn't allow
to sleep, because the ->release() is run via call_rcu().

Fixes this issue by moving put disk reference into hd_struct_free_work()

Fixes: e8c7d14ac6c3 ("block: revert back to synchronous request_queue removal")
Reported-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Tested-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/partitions/core.c b/block/partitions/core.c
index e62a98a..5a18c8e 100644 (file)
--- a/block/partitions/core.c
+++ b/block/partitions/core.c
@@ -278,6 +278,15 @@ static void hd_struct_free_work(struct work_struct *work)
 {
        struct hd_struct *part =
                container_of(to_rcu_work(work), struct hd_struct, rcu_work);
+       struct gendisk *disk = part_to_disk(part);
+
+       /*
+        * Release the disk reference acquired in delete_partition here.
+        * We can't release it in hd_struct_free because the final put_device
+        * needs process context and thus can't be run directly from a
+        * percpu_ref ->release handler.
+        */
+       put_device(disk_to_dev(disk));
 
        part->start_sect = 0;
        part->nr_sects = 0;
@@ -293,7 +302,6 @@ static void hd_struct_free(struct percpu_ref *ref)
                rcu_dereference_protected(disk->part_tbl, 1);
 
        rcu_assign_pointer(ptbl->last_lookup, NULL);
-       put_device(disk_to_dev(disk));
 
        INIT_RCU_WORK(&part->rcu_work, hd_struct_free_work);
        queue_rcu_work(system_wq, &part->rcu_work);