linux-kernel - Re: [PATCH] block: don't decrement flush request refcount if it's state is idle in flush_end

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Date:   Fri, 13 Aug 2021 20:34:17 +0800
From:   "yukuai (C)" <yukuai3@...wei.com>
To:     <axboe@...nel.dk>
CC:     <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <yi.zhang@...wei.com>
Subject: Re: [PATCH] block: don't decrement flush request refcount if it's
 state is idle in flush_end_io()

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:
>> 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 <yukuai3@...wei.com>
>> ---
>>   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;
>>
> .
>