[PATCH] block: don't decrement flush request refcount if it's state is idle in flush_end_io()

flush_end_io() currently decrement request refcount unconditionally.
However, it's possible that the request is already idle and it's
refcount is zero since that flush_end_io() can be called concurrently.

For example, nbd_clear_que() can be called concurrently with normal
io completion or io timeout.

Thus check idle before decrement to avoid refcount_t underflow
warning.

Signed-off-by: Yu Kuai <redacted>
---
 block/blk-flush.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/blk-flush.c b/block/blk-flush.c
index 1002f6c58181..9b65dc43702c 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c

@@ -222,7 +222,8 @@ static void flush_end_io(struct request *flush_rq, blk_status_t error)
 	/* release the tag's ownership to the req cloned from */
 	spin_lock_irqsave(&fq->mq_flush_lock, flags);
 
-	if (!refcount_dec_and_test(&flush_rq->ref)) {
+	if (blk_mq_rq_state(flush_rq) == MQ_RQ_IDLE ||
+	    !refcount_dec_and_test(&flush_rq->ref)) {
 		fq->rq_status = error;
 		spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
 		return;

-- 
2.31.1

On Sun, Aug 08, 2021 at 03:03:30PM +0800, Yu Kuai wrote:

It is driver's bug to finish one already ended request, so please
fix the driver instead.

Thanks,
Ming

Hi, jens

Can you please consider to apply this patch?

Thanks
Kuai

On 2021/08/08 15:03, Yu Kuai wrote:

Please ignore this email, I reply to the wrong wmail.

Sincerely apologize
Kuai

在 2021/08/13 17:40, yukuai (C) 写道:

Hi, jens

Can you please consider to apply this patch?

Thanks
Kuai

On 2021/08/08 15:03, Yu Kuai wrote:

quoted

flush_end_io() currently decrement request refcount unconditionally.
However, it's possible that the request is already idle and it's
refcount is zero since that flush_end_io() can be called concurrently.

For example, nbd_clear_que() can be called concurrently with normal
io completion or io timeout.

Thus check idle before decrement to avoid refcount_t underflow
warning.

Signed-off-by: Yu Kuai <redacted>
---
  block/blk-flush.c | 3 ++-
  1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/blk-flush.c b/block/blk-flush.c
index 1002f6c58181..9b65dc43702c 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c

@@ -222,7 +222,8 @@ static void flush_end_io(struct request *flush_rq, 

blk_status_t error)
      /* release the tag's ownership to the req cloned from */
      spin_lock_irqsave(&fq->mq_flush_lock, flags);
-    if (!refcount_dec_and_test(&flush_rq->ref)) {
+    if (blk_mq_rq_state(flush_rq) == MQ_RQ_IDLE ||
+        !refcount_dec_and_test(&flush_rq->ref)) {
          fq->rq_status = error;
          spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
          return;

.