Re: [PATCH 07/11] vfio/platform: Remove dead assignment in vfio_intp_interrupt()

[Alex Williamson]

On Thu, 13 Aug 2020 15:37:08 +0800
Chen Qun <kuhn.chenqun@huawei.com> wrote:

> Clang static code analyzer show warning:
> hw/vfio/platform.c:239:9: warning: Value stored to 'ret' is never read
>         ret = event_notifier_test_and_clear(intp->interrupt);
>         ^     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Reported-by: Euler Robot <euler.robot@huawei.com>
> Signed-off-by: Chen Qun <kuhn.chenqun@huawei.com>
> ---
> Cc: Alex Williamson <alex.williamson@redhat.com>
> Cc: Eric Auger <eric.auger@redhat.com>
> ---
>  hw/vfio/platform.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/vfio/platform.c b/hw/vfio/platform.c
> index ac2cefc9b1..869ed2c39d 100644
> --- a/hw/vfio/platform.c
> +++ b/hw/vfio/platform.c
> @@ -236,7 +236,7 @@ static void vfio_intp_interrupt(VFIOINTp *intp)
>          trace_vfio_intp_interrupt_set_pending(intp->pin);
>          QSIMPLEQ_INSERT_TAIL(&vdev->pending_intp_queue,
>                               intp, pqnext);
> -        ret = event_notifier_test_and_clear(intp->interrupt);
> +        event_notifier_test_and_clear(intp->interrupt);
>          return;
>      }

Testing that an event is pending in our notifier is generally a
prerequisite to doing anything in the interrupt handler, I don't
understand why we're just consuming it and ignoring the return value.
The above is in the delayed handling branch of the function, but the
normal non-delayed path would only go on to error_report() if the
notifier is not pending and then inject an interrupt anyway.  This all
seems rather suspicious and it's a unique pattern among the vfio
callers of this function.  Is there a more fundamental bug that this
function should perform this test once and return without doing
anything if it's called spuriously, ie. without a notifier pending?
Thanks,

Alex