Re: [PATCH for-6.1? v2 6/7] mirror: Check job_is_cancelled() earlier

[Kevin Wolf <kwolf@redhat.com>]

Am 26.07.2021 um 16:46 hat Max Reitz geschrieben:
> We must check whether the job is force-cancelled early in our main loop,
> most importantly before any `continue` statement.  For example, we used
> to have `continue`s before our current checking location that are
> triggered by `mirror_flush()` failing.  So, if `mirror_flush()` kept
> failing, force-cancelling the job would not terminate it.
> 
> A job being force-cancelled should be treated the same as the job having
> failed, so put the check in the same place where we check `s->ret < 0`.
> 
> Buglink: https://gitlab.com/qemu-project/qemu/-/issues/462
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block/mirror.c | 7 +------
>  1 file changed, 1 insertion(+), 6 deletions(-)
> 
> diff --git a/block/mirror.c b/block/mirror.c
> index 72e02fa34e..46d1a1e5a2 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -993,7 +993,7 @@ static int coroutine_fn mirror_run(Job *job, Error **errp)
>              mirror_wait_for_any_operation(s, true);
>          }
>  
> -        if (s->ret < 0) {
> +        if (s->ret < 0 || job_is_cancelled(&s->common.job)) {
>              ret = s->ret;
>              goto immediate_exit;
>          }
> @@ -1078,8 +1078,6 @@ static int coroutine_fn mirror_run(Job *job, Error **errp)
>              break;
>          }
>  
> -        ret = 0;
> -
>          if (job_is_ready(&s->common.job) && !should_complete) {
>              delay_ns = (s->in_flight == 0 &&
>                          cnt == 0 ? BLOCK_JOB_SLICE_TIME : 0);
> @@ -1087,9 +1085,6 @@ static int coroutine_fn mirror_run(Job *job, Error **errp)
>          trace_mirror_before_sleep(s, cnt, job_is_ready(&s->common.job),
>                                    delay_ns);
>          job_sleep_ns(&s->common.job, delay_ns);
> -        if (job_is_cancelled(&s->common.job)) {
> -            break;
> -        }

I think it was intentional that the check is here because it means
skipping the job_sleep_ns() and instead cancelling immediately, and we
probably still want that. Between your check above and here, the
coroutine can yield, so cancellation could have been newly requested.

So have the check in both places, I guess? And a comment to explain why
neither is redundant.

>          s->last_pause_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
>      }

Kevin