block: null_blk: fix use after free

entry(cmd->ll_list) may belong to new request once end_cmd()
returns, so fix the bug with the patch.

Without the change, it is easy to observe oops when
doing null_blk(timer) test.

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/drivers/block/null_blk.c b/drivers/block/null_blk.c
index 8e7e3a0b0d24..e932398588aa 100644
--- a/drivers/block/null_blk.c
+++ b/drivers/block/null_blk.c
@@ -203,8 +203,8 @@ static enum hrtimer_restart null_cmd_timer_expired(struct hrtimer *timer)
                 entry = llist_reverse_order(entry);
                 do {
                         cmd = container_of(entry, struct nullb_cmd, ll_list);
-                        end_cmd(cmd);
                         entry = entry->next;
+                        end_cmd(cmd);
                 } while (entry);
         }