Am 05/08/2022 um 11:12 schrieb Kevin Wolf:
> Am 25.07.2022 um 09:38 hat Emanuele Giuseppe Esposito geschrieben:
>> In order to make it thread safe, implement a "fake rwlock",
>> where we allow reads under BQL *or* job_mutex held, but
>> writes only under BQL *and* job_mutex.
>
> Oh, so the "or BQL" part is only for job.aio_context? Okay.
>
>> The only write we have is in child_job_set_aio_ctx, which always
>> happens under drain (so the job is paused).
>> For this reason, introduce job_set_aio_context and make sure that
>> the context is set under BQL, job_mutex and drain.
>> Also make sure all other places where the aiocontext is read
>> are protected.
>>
>> Note: at this stage, job_{lock/unlock} and job lock guard macros
>> are *nop*.
>>
>> Suggested-by: Paolo Bonzini <pbonz...@redhat.com>
>> Signed-off-by: Emanuele Giuseppe Esposito <eespo...@redhat.com>
>> Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com>
>> ---
>> block/replication.c | 6 ++++--
>> blockjob.c | 3 ++-
>> include/qemu/job.h | 19 ++++++++++++++++++-
>> job.c | 12 ++++++++++++
>> 4 files changed, 36 insertions(+), 4 deletions(-)
>>
>> diff --git a/block/replication.c b/block/replication.c
>> index 55c8f894aa..2189863df1 100644
>> --- a/block/replication.c
>> +++ b/block/replication.c
>> @@ -148,8 +148,10 @@ static void replication_close(BlockDriverState *bs)
>> }
>> if (s->stage == BLOCK_REPLICATION_FAILOVER) {
>> commit_job = &s->commit_job->job;
>> - assert(commit_job->aio_context == qemu_get_current_aio_context());
>> - job_cancel_sync(commit_job, false);
>> + WITH_JOB_LOCK_GUARD() {
>> + assert(commit_job->aio_context ==
>> qemu_get_current_aio_context());
>> + job_cancel_sync_locked(commit_job, false);
>> + }
>> }
>
> .bdrv_close runs under the BQL, so why is this needed? Maybe a
> GLOBAL_STATE_CODE() annotation would be helpful, though.
I think I left it because it would be confusing to leave a _locked
function without the job lock. I'll add the GLOBAL_STATE_CODE anyways.
>
>> if (s->mode == REPLICATION_MODE_SECONDARY) {
>> diff --git a/blockjob.c b/blockjob.c
>> index 96fb9d9f73..9ff2727025 100644
>> --- a/blockjob.c
>> +++ b/blockjob.c
>> @@ -162,12 +162,13 @@ static void child_job_set_aio_ctx(BdrvChild *c,
>> AioContext *ctx,
>> bdrv_set_aio_context_ignore(sibling->bs, ctx, ignore);
>> }
>>
>> - job->job.aio_context = ctx;
>> + job_set_aio_context(&job->job, ctx);
>> }
>>
>> static AioContext *child_job_get_parent_aio_context(BdrvChild *c)
>> {
>> BlockJob *job = c->opaque;
>> + assert(qemu_in_main_thread());
>
> Any reason not to use GLOBAL_STATE_CODE()?
4 months ago GLOBAL_STATE_CODE did not exist yet, and I didn't think
about updating it :)
>
>> return job->job.aio_context;
>> }
>> + /* protect against read in job_do_yield_locked */
>> + JOB_LOCK_GUARD();
>> + /* ensure the coroutine is quiescent while the AioContext is changed */
>> + assert(job->pause_count > 0);
>
> job->pause_count only shows that pausing was requested. The coroutine is
> only really quiescent if job->busy == false, too.
>
> Or maybe job->paused is actually the one you want here.
I think job->paused works too.
Emanuele
