[PATCH] block: null_blk: fix use after free

[Ming Lei]

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@xxxxxxxxx>
---
 drivers/block/null_blk.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/null_blk.c b/drivers/block/null_blk.c
index 8e7e3a0..e932398 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);
 	}
 
-- 
1.7.9.5

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