| Message ID | 20211006151940.214590-9-hreitz@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | mirror: Handle errors after READY cancel | expand |
On Wed, Oct 06, 2021 at 05:19:35PM +0200, Hanna 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 Is this reference still accurate with the addition of new patch 7? > cancellation request as a request for immediate termination), and add > job_cancel_requested() 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. > > Finally, here is a justification for how different job_is_cancelled() > invocations are treated by this patch: ... > - job_update_rc(), job_finalize_single(), job_finish_sync(): These > functions are all called after the job has left its main loop. The > mirror job (the only job that can be soft-cancelled) will clear > .cancelled before leaving the main loop if it has been > soft-cancelled. Therefore, these functions will observe .cancelled > to be true only if the job has been force-cancelled. We can > continue to use job_is_cancelled(). > (Furthermore, conceptually, a soft-cancelled mirror job should not > report to have been cancelled. It should report completion (see > also the block-job-cancel QAPI documentation). Therefore, it makes > sense for these functions not to distinguish between a > soft-cancelled mirror job and a job that has completed as normal.) Thanks for the careful explanation. > > Buglink: https://gitlab.com/qemu-project/qemu/-/issues/462 > Signed-off-by: Hanna Reitz <hreitz@redhat.com> > --- > include/qemu/job.h | 8 +++++++- > block/mirror.c | 10 ++++------ > job.c | 14 ++++++++++++-- > 3 files changed, 23 insertions(+), 9 deletions(-) The commit message is loads longer than the patch itself, but for good reason. Reviewed-by: Eric Blake <eblake@redhat.com>
10/6/21 18:19, Hanna 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_requested() 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. > > Finally, here is a justification for how different job_is_cancelled() > invocations are treated by this patch: > > - block/mirror.c (mirror_run()): > - The first invocation is a while loop that should loop until the job > has been cancelled or scheduled for completion. What kind of cancel > does not matter, only the fact that the job is supposed to end. > > - The second invocation wants to know whether the job has been > soft-cancelled. Calling job_cancel_requested() is a bit too broad, > but if the job were force-cancelled, we should leave the main loop > as soon as possible anyway, so this should not matter here. > > - The last two invocations already check force_cancel, so they should > continue to use job_is_cancelled(). > > - block/backup.c, block/commit.c, block/stream.c, anything in tests/: > These jobs know only force-cancel, so there is no difference between > job_is_cancelled() and job_cancel_requested(). We can continue using > job_is_cancelled(). > > - job.c: > - job_pause_point(), job_yield(), job_sleep_ns(): Only force-cancelled > jobs should be prevented from being paused. Continue using job_is_cancelled(). > > - job_update_rc(), job_finalize_single(), job_finish_sync(): These > functions are all called after the job has left its main loop. The > mirror job (the only job that can be soft-cancelled) will clear > .cancelled before leaving the main loop if it has been > soft-cancelled. Therefore, these functions will observe .cancelled > to be true only if the job has been force-cancelled. We can > continue to use job_is_cancelled(). > (Furthermore, conceptually, a soft-cancelled mirror job should not > report to have been cancelled. It should report completion (see > also the block-job-cancel QAPI documentation). Therefore, it makes > sense for these functions not to distinguish between a > soft-cancelled mirror job and a job that has completed as normal.) > > - job_completed_txn_abort(): All jobs other than @job have been > force-cancelled. job_is_cancelled() must be true for them. > Regarding @job itself: job_completed_txn_abort() is mostly called > when the job's return value is not 0. A soft-cancelled mirror has a > return value of 0, and so will not end up here then. > However, job_cancel() invokes job_completed_txn_abort() if the job > has been deferred to the main loop, which is mostly the case for > completed jobs (which skip the assertion), but not for sure. > To be safe, use job_cancel_requested() in this assertion. > > - job_complete(): This is function eventually invoked by the user > (through qmp_block_job_complete() or qmp_job_complete(), or > job_complete_sync(), which comes from qemu-img). The intention here > is to prevent a user from invoking job-complete after the job has > been cancelled. This should also apply to soft cancelling: After a > mirror job has been soft-cancelled, the user should not be able to > decide otherwise and have it complete as normal (i.e. pivoting to > the target). > > - job_cancel(): Both functions are equivalent (see comment there), but > we want to use job_is_cancelled(), because this shows that we call > job_completed_txn_abort() only for force-cancelled jobs. (As > explained for job_update_rc(), soft-cancelled jobs should be treated > as if they have completed as normal.) > > Buglink:https://gitlab.com/qemu-project/qemu/-/issues/462 > Signed-off-by: Hanna Reitz<hreitz@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
diff --git a/include/qemu/job.h b/include/qemu/job.h index 90f6abbd6a..6e67b6977f 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 010b9e1672..2d9642cb00 100644 --- a/block/mirror.c +++ b/block/mirror.c @@ -943,7 +943,7 @@ 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; @@ -1050,7 +1050,7 @@ 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); } @@ -1094,7 +1094,7 @@ 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); @@ -1106,9 +1106,7 @@ 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)); assert(need_drain); mirror_wait_for_all_io(s); } diff --git a/job.c b/job.c index 44e741ebd4..b0cf2d8374 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; +} + +bool job_cancel_requested(Job *job) { return job->cancelled; } @@ -798,7 +803,7 @@ static void job_completed_txn_abort(Job *job) ctx = other_job->aio_context; aio_context_acquire(ctx); if (!job_is_completed(other_job)) { - assert(job_is_cancelled(other_job)); + assert(job_cancel_requested(other_job)); job_finish_sync(other_job, NULL, NULL); } job_finalize_single(other_job); @@ -977,6 +982,11 @@ void job_cancel(Job *job, bool force) * job_cancel_async() ignores soft-cancel requests for jobs * that are already done (i.e. deferred to the main loop). We * have to check again whether the job is really cancelled. + * (job_cancel_requested() and job_is_cancelled() are equivalent + * here, because job_cancel_async() will make soft-cancel + * requests no-ops when deferred_to_main_loop is true. We + * choose to call job_is_cancelled() to show that we invoke + * job_completed_txn_abort() only for force-cancelled jobs.) */ if (job_is_cancelled(job)) { job_completed_txn_abort(job); @@ -1044,7 +1054,7 @@ 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;
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_requested() 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. Finally, here is a justification for how different job_is_cancelled() invocations are treated by this patch: - block/mirror.c (mirror_run()): - The first invocation is a while loop that should loop until the job has been cancelled or scheduled for completion. What kind of cancel does not matter, only the fact that the job is supposed to end. - The second invocation wants to know whether the job has been soft-cancelled. Calling job_cancel_requested() is a bit too broad, but if the job were force-cancelled, we should leave the main loop as soon as possible anyway, so this should not matter here. - The last two invocations already check force_cancel, so they should continue to use job_is_cancelled(). - block/backup.c, block/commit.c, block/stream.c, anything in tests/: These jobs know only force-cancel, so there is no difference between job_is_cancelled() and job_cancel_requested(). We can continue using job_is_cancelled(). - job.c: - job_pause_point(), job_yield(), job_sleep_ns(): Only force-cancelled jobs should be prevented from being paused. Continue using job_is_cancelled(). - job_update_rc(), job_finalize_single(), job_finish_sync(): These functions are all called after the job has left its main loop. The mirror job (the only job that can be soft-cancelled) will clear .cancelled before leaving the main loop if it has been soft-cancelled. Therefore, these functions will observe .cancelled to be true only if the job has been force-cancelled. We can continue to use job_is_cancelled(). (Furthermore, conceptually, a soft-cancelled mirror job should not report to have been cancelled. It should report completion (see also the block-job-cancel QAPI documentation). Therefore, it makes sense for these functions not to distinguish between a soft-cancelled mirror job and a job that has completed as normal.) - job_completed_txn_abort(): All jobs other than @job have been force-cancelled. job_is_cancelled() must be true for them. Regarding @job itself: job_completed_txn_abort() is mostly called when the job's return value is not 0. A soft-cancelled mirror has a return value of 0, and so will not end up here then. However, job_cancel() invokes job_completed_txn_abort() if the job has been deferred to the main loop, which is mostly the case for completed jobs (which skip the assertion), but not for sure. To be safe, use job_cancel_requested() in this assertion. - job_complete(): This is function eventually invoked by the user (through qmp_block_job_complete() or qmp_job_complete(), or job_complete_sync(), which comes from qemu-img). The intention here is to prevent a user from invoking job-complete after the job has been cancelled. This should also apply to soft cancelling: After a mirror job has been soft-cancelled, the user should not be able to decide otherwise and have it complete as normal (i.e. pivoting to the target). - job_cancel(): Both functions are equivalent (see comment there), but we want to use job_is_cancelled(), because this shows that we call job_completed_txn_abort() only for force-cancelled jobs. (As explained for job_update_rc(), soft-cancelled jobs should be treated as if they have completed as normal.) Buglink: https://gitlab.com/qemu-project/qemu/-/issues/462 Signed-off-by: Hanna Reitz <hreitz@redhat.com> --- include/qemu/job.h | 8 +++++++- block/mirror.c | 10 ++++------ job.c | 14 ++++++++++++-- 3 files changed, 23 insertions(+), 9 deletions(-)