Re: [PATCH for-6.1? v2 5/7] job: Add job_cancel_requested()

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

27.07.2021 18:39, Max Reitz wrote:
> On 27.07.21 15:04, Vladimir Sementsov-Ogievskiy wrote:
>> 26.07.2021 17:46, Max Reitz wrote:
>>> Most callers of job_is_cancelled() actually want to know whether the job
>>> is on its way to immediate termination.  For example, we refuse to pause
>>> jobs that are cancelled; but this only makes sense for jobs that are
>>> really actually cancelled.
>>>
>>> A mirror job that is cancelled during READY with force=false should
>>> absolutely be allowed to pause.  This "cancellation" (which is actually
>>> a kind of completion) may take an indefinite amount of time, and so
>>> should behave like any job during normal operation.  For example, with
>>> on-target-error=stop, the job should stop on write errors.  (In
>>> contrast, force-cancelled jobs should not get write errors, as they
>>> should just terminate and not do further I/O.)
>>>
>>> Therefore, redefine job_is_cancelled() to only return true for jobs that
>>> are force-cancelled (which as of HEAD^ means any job that interprets the
>>> cancellation request as a request for immediate termination), and add
>>> job_cancel_request() as the general variant, which returns true for any
>>
>> job_cancel_requested()
>>
>>> jobs which have been requested to be cancelled, whether it be
>>> immediately or after an arbitrarily long completion phase.
>>>
>>> Buglink: https://gitlab.com/qemu-project/qemu/-/issues/462
>>> Signed-off-by: Max Reitz <mreitz@redhat.com>
>>> ---
>>>   include/qemu/job.h |  8 +++++++-
>>>   block/mirror.c     | 10 ++++------
>>>   job.c              |  7 ++++++-
>>>   3 files changed, 17 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/include/qemu/job.h b/include/qemu/job.h
>>> index 8aa90f7395..032edf3c5f 100644
>>> --- a/include/qemu/job.h
>>> +++ b/include/qemu/job.h
>>> @@ -436,9 +436,15 @@ const char *job_type_str(const Job *job);
>>>   /** Returns true if the job should not be visible to the management layer. */
>>>   bool job_is_internal(Job *job);
>>>   -/** Returns whether the job is scheduled for cancellation. */
>>> +/** Returns whether the job is being cancelled. */
>>>   bool job_is_cancelled(Job *job);
>>>   +/**
>>> + * Returns whether the job is scheduled for cancellation (at an
>>> + * indefinite point).
>>> + */
>>> +bool job_cancel_requested(Job *job);
>>> +
>>>   /** Returns whether the job is in a completed state. */
>>>   bool job_is_completed(Job *job);
>>>   diff --git a/block/mirror.c b/block/mirror.c
>>> index e93631a9f6..72e02fa34e 100644
>>> --- a/block/mirror.c
>>> +++ b/block/mirror.c
>>> @@ -936,7 +936,7 @@ static int coroutine_fn mirror_run(Job *job, Error **errp)
>>>           /* Transition to the READY state and wait for complete. */
>>>           job_transition_to_ready(&s->common.job);
>>>           s->actively_synced = true;
>>> -        while (!job_is_cancelled(&s->common.job) && !s->should_complete) {
>>> +        while (!job_cancel_requested(&s->common.job) && !s->should_complete) {
>>>               job_yield(&s->common.job);
>>>           }
>>>           s->common.job.cancelled = false;
>>> @@ -1043,7 +1043,7 @@ static int coroutine_fn mirror_run(Job *job, Error **errp)
>>>               }
>>>                 should_complete = s->should_complete ||
>>> -                job_is_cancelled(&s->common.job);
>>> +                job_cancel_requested(&s->common.job);
>>>               cnt = bdrv_get_dirty_count(s->dirty_bitmap);
>>>           }
>>>   @@ -1087,7 +1087,7 @@ 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) && s->common.job.force_cancel) {
>>> +        if (job_is_cancelled(&s->common.job)) {
>>>               break;
>>>           }
>>>           s->last_pause_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
>>> @@ -1099,9 +1099,7 @@ immediate_exit:
>>>            * or it was cancelled prematurely so that we do not guarantee that
>>>            * the target is a copy of the source.
>>>            */
>>> -        assert(ret < 0 ||
>>> -               (s->common.job.force_cancel &&
>>> -                job_is_cancelled(&s->common.job)));
>>> +        assert(ret < 0 || job_is_cancelled(&s->common.job));
> 
> (As a note, I hope this does the job regarding your suggestions for patch 4. :))
> 
>>>           assert(need_drain);
>>>           mirror_wait_for_all_io(s);
>>>       }
>>> diff --git a/job.c b/job.c
>>> index e78d893a9c..dba17a680f 100644
>>> --- a/job.c
>>> +++ b/job.c
>>> @@ -216,6 +216,11 @@ const char *job_type_str(const Job *job)
>>>   }
>>>     bool job_is_cancelled(Job *job)
>>> +{
>>> +    return job->cancelled && job->force_cancel;
>>
>> can job->cancelled be false when job->force_cancel is true ? I think not and worth an assertion here. Something like
>>
>> if (job->force_cancel) {
>>    assert(job->cancelled);
>>    return true;
>> }
>>
>> return false;
> 
> Sounds good, why not.
> 
>>
>>> +}
>>> +
>>> +bool job_cancel_requested(Job *job)
>>>   {
>>>       return job->cancelled;
>>>   }
>>> @@ -1015,7 +1020,7 @@ void job_complete(Job *job, Error **errp)
>>>       if (job_apply_verb(job, JOB_VERB_COMPLETE, errp)) {
>>>           return;
>>>       }
>>> -    if (job_is_cancelled(job) || !job->driver->complete) {
>>> +    if (job_cancel_requested(job) || !job->driver->complete) {
>>>           error_setg(errp, "The active block job '%s' cannot be completed",
>>>                      job->id);
>>>           return;
>>>
>>
>> I think it's a correct change, although there may be unexpected side-effects, it's hard to imagine all consequences of changing job_is_cancelled() semantics called in several places in job.c.

For example: so we now don't set -ECANCELED in job_update_rc for soft-cancel..

This mean that job_finalize_single() will call job_commit instead of job_abort, and job_commit may do some graph changes, which shouldn't happen for soft-cancel

> 
> Yeah.  Targeting 6.2, I don’t have a bad feeling about it, though.
> 
>> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> 
> Thanks for the review, by the way!
> 
> Max
> 


-- 
Best regards,
Vladimir