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4/6] job: Add job_cancel_requested() To: Vladimir Sementsov-Ogievskiy , qemu-block@nongnu.org References: <20210722122627.29605-1-mreitz@redhat.com> <20210722122627.29605-5-mreitz@redhat.com> From: Max Reitz Message-ID: <32463d65-834c-64ba-aab4-36f1810ddb43@redhat.com> Date: Mon, 26 Jul 2021 09:09:09 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mreitz@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Received-SPF: pass client-ip=170.10.133.124; envelope-from=mreitz@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -45 X-Spam_score: -4.6 X-Spam_bar: ---- X-Spam_report: (-4.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.719, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-1.091, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , John Snow , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 22.07.21 19:58, Vladimir Sementsov-Ogievskiy wrote: > 22.07.2021 15:26, 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) > > You have to repeat that this "cancel" is not "cancel". > > So, the whole problem is that feature of mirror, on cancel in READY > state do not cancel but do some specific kind of completion. > > You try to make this thing correctly handled on generic layer.. > > Did you consider instead just drop the feature from generic layer? So > that all *cancel* functions always do force-cancel. Then the internal > implementation become a lot clearer. Yes, I considered that, and I’ve decided against it (for now), because such a change would obviously be an incompatible change.  It would require a deprecation period, and so we would need to fix this bug now anyway. > But we have to support the qmp block-job-cancel of READY mirror (and > commit) with force=false. > > We can do it as an exclusion in qmp_block_job_cancel, something like: > > if (job is mirror or commit AND it's ready AND force = false) >    mirror_soft_cancel(...); > else >    job_cancel(...); I didn’t consider such a hack, though.  I don’t like it.  If we think that we should change our approach because mirror’s soft cancel is actually a completion mode, and the current situation is too confusing, such a change should be user-visible, too.  (I think there was this idea of having job-specific flags or parameters you could change at runtime, and so you’d just change the “pivot” parameter between true or false.) Also, I don’t know whether this would really make anything “a lot” easier.  After this series job_is_cancelled() already tells the true story, so all we could really change is to drop force_cancel and unify the “s->should_complete || job_cancel_requested()” conditions in block/mirror.c into one variable.  So when I considered making cancel exclusively force-cancel jobs, I thought it wouldn’t actually be worth it in practice. >> 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 >> 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 >> --- > > [..] > >> --- 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; >> +} >> + >> +bool job_cancel_requested(Job *job) >>   { >>       return job->cancelled; >>   } >> @@ -650,7 +655,7 @@ static void job_conclude(Job *job) >>     static void job_update_rc(Job *job) >>   { >> -    if (!job->ret && job_is_cancelled(job)) { >> +    if (!job->ret && job_cancel_requested(job)) { > > Why not job_is_cancelled() here? > > So in case of mirror other kind of completion we set ret to -ECANCELED? I thought the return value is a user-visible thing, so I left it as-is. Seems I was wrong, more below. >>           job->ret = -ECANCELED; >>       } >>       if (job->ret) { >> @@ -704,7 +709,7 @@ static int job_finalize_single(Job *job) >>         /* Emit events only if we actually started */ >>       if (job_started(job)) { >> -        if (job_is_cancelled(job)) { >> +        if (job_cancel_requested(job)) { >>               job_event_cancelled(job); > > Same question here.. Shouldn't mirror report COMPLETED event in case > of not-force cancelled in READY state? Same here, I thought this is user-visible, nothing internal, so I should leave it as-is. Now I see that cancelling mirror post-READY indeed should result in a COMPLETED event.  So I’m actually not exactly sure how mirror does that, despite this code here (which functionally isn’t changed by this patch), but it’s absolutely true that job_is_cancelled() would be more appropriate here. (No iotest failed, so I thought this change was right.  Well.) >>           } else { >>               job_event_completed(job); >> @@ -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; >> @@ -1043,7 +1048,7 @@ int job_finish_sync(Job *job, void >> (*finish)(Job *, Error **errp), Error **errp) >>       AIO_WAIT_WHILE(job->aio_context, >>                      (job_enter(job), !job_is_completed(job))); >>   -    ret = (job_is_cancelled(job) && job->ret == 0) ? -ECANCELED : >> job->ret; >> +    ret = (job_cancel_requested(job) && job->ret == 0) ? -ECANCELED >> : job->ret; So here it should probably stay a job_is_cancelled(), too. Max >>       job_unref(job); >>       return ret; >>   } >> > >