Re: [PATCH V4 1/4] block: avoid double io accounting for flush request

[Ming Lei <ming.lei@redhat.com>]

On Thu, Apr 29, 2021 at 07:51:37PM -0700, Bart Van Assche wrote:
> On 4/28/21 7:34 PM, Ming Lei wrote:
> > For flush request, rq->end_io() may be called two times, one is from
> > timeout handling(blk_mq_check_expired()), another is from normal
> > completion(__blk_mq_end_request()).
> > 
> > Move blk_account_io_flush() after flush_rq->ref drops to zero, so
> > io accounting can be done just once for flush request.
> > 
> > Signed-off-by: Ming Lei <ming.lei@redhat.com>
> > ---
> >  block/blk-flush.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> > 
> > diff --git a/block/blk-flush.c b/block/blk-flush.c
> > index 7942ca6ed321..1002f6c58181 100644
> > --- a/block/blk-flush.c
> > +++ b/block/blk-flush.c
> > @@ -219,8 +219,6 @@ static void flush_end_io(struct request *flush_rq, blk_status_t error)
> >  	unsigned long flags = 0;
> >  	struct blk_flush_queue *fq = blk_get_flush_queue(q, flush_rq->mq_ctx);
> >  
> > -	blk_account_io_flush(flush_rq);
> > -
> >  	/* release the tag's ownership to the req cloned from */
> >  	spin_lock_irqsave(&fq->mq_flush_lock, flags);
> >  
> > @@ -230,6 +228,7 @@ static void flush_end_io(struct request *flush_rq, blk_status_t error)
> >  		return;
> >  	}
> >  
> > +	blk_account_io_flush(flush_rq);
> >  	/*
> >  	 * Flush request has to be marked as IDLE when it is really ended
> >  	 * because its .end_io() is called from timeout code path too for
> 
> How about adding the following:
> 
> Fixes: b68663186577 ("block: add iostat counters for flush requests")

Yeah, good point, thanks!

Jens, I guess you may cover that, or please let me know if V5 is needed. 

Thanks, 
Ming