Re: [Qemu-devel] [Qemu-block] [PATCH v2] qemu-img: fix in-flight count for qemu-img bench

[John Snow <jsnow@redhat.com>]

On 12/07/2016 10:08 AM, Paolo Bonzini wrote:
> With aio=native (qemu-img bench -n) one or more requests can be completed
> when a new request is submitted.  This in turn can cause bench_cb to
> recurse before b->in_flight is updated.  This causes multiple I/Os
> to be submitted with the same offset and, furthermore, the blk_aio_*
> coroutines are never freed and qemu-img aborts.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  qemu-img.c | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/qemu-img.c b/qemu-img.c
> index 6949b73..5df66fe 100644
> --- a/qemu-img.c
> +++ b/qemu-img.c
> @@ -3559,20 +3559,23 @@ static void bench_cb(void *opaque, int ret)
>      }
>  
>      while (b->n > b->in_flight && b->in_flight < b->nrreq) {
> +        int64_t offset = b->offset;
> +        /* blk_aio_* might look for completed I/Os and kick bench_cb
> +         * again, so make sure this operation is counted by in_flight
> +         * and b->offset is ready for the next submission.
> +         */
> +        b->in_flight++;
> +        b->offset += b->step;
> +        b->offset %= b->image_size;
>          if (b->write) {
> -            acb = blk_aio_pwritev(b->blk, b->offset, b->qiov, 0,
> -                                  bench_cb, b);
> +            acb = blk_aio_pwritev(b->blk, offset, b->qiov, 0, bench_cb, b);
>          } else {
> -            acb = blk_aio_preadv(b->blk, b->offset, b->qiov, 0,
> -                                 bench_cb, b);
> +            acb = blk_aio_preadv(b->blk, offset, b->qiov, 0, bench_cb, b);
>          }
>          if (!acb) {
>              error_report("Failed to issue request");
>              exit(EXIT_FAILURE);
>          }
> -        b->in_flight++;
> -        b->offset += b->step;
> -        b->offset %= b->image_size;
>      }
>  }
>  
> 

Reviewed-by: John Snow <jsnow@redhat.com>