Am 11/07/2022 um 16:19 schrieb Vladimir Sementsov-Ogievskiy:
> On 7/6/22 23:15, Emanuele Giuseppe Esposito wrote:
>> 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.
>>
>> The only write we have is in child_job_set_aio_ctx
>
> also in job_create of course, but it seems safe anyway
>
>> , 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);
>> + }
>> }
>> if (s->mode == REPLICATION_MODE_SECONDARY) {
>> diff --git a/blockjob.c b/blockjob.c
>> index bce05a9096..0d120ed126 100644
>> --- a/blockjob.c
>> +++ b/blockjob.c
>> @@ -166,12 +166,13 @@ 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());
>> return job->job.aio_context;
>> }
>> diff --git a/include/qemu/job.h b/include/qemu/job.h
>> index 5709e8d4a8..c144aabefc 100644
>> --- a/include/qemu/job.h
>> +++ b/include/qemu/job.h
>> @@ -77,7 +77,12 @@ typedef struct Job {
>> /** Protected by AioContext lock */
>> - /** AioContext to run the job coroutine in */
>> + /**
>> + * AioContext to run the job coroutine in.
>> + * This field can be read when holding either the BQL (so we are in
>> + * the main loop) or the job_mutex.
>> + * It can be only written when we hold *both* BQL and job_mutex.
>> + */
>> AioContext *aio_context;
>> /** Reference count of the block job */
>> @@ -741,4 +746,16 @@ int job_finish_sync(Job *job, void (*finish)(Job
>> *, Error **errp),
>> int job_finish_sync_locked(Job *job, void (*finish)(Job *, Error
>> **errp),
>> Error **errp);
>> +/**
>> + * Sets the @job->aio_context.
>> + * Called with job_mutex *not* held.
>> + *
>> + * This function must run in the main thread to protect against
>> + * concurrent read in job_finish_sync_locked(),
>> + * takes the job_mutex lock to protect against the read in
>> + * job_do_yield_locked(), and must be called when the coroutine
>> + * is quiescent.
>> + */
>> +void job_set_aio_context(Job *job, AioContext *ctx);
>> +
>> #endif
>> diff --git a/job.c b/job.c
>> index 405f39566b..66cae82593 100644
>> --- a/job.c
>> +++ b/job.c
>> @@ -394,6 +394,17 @@ Job *job_get(const char *id)
>> return job_get_locked(id);
>> }
>> +void job_set_aio_context(Job *job, AioContext *ctx)
>> +{
>> + /* protect against read in job_finish_sync_locked and job_start */
>> + assert(qemu_in_main_thread());
>> + /* 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->aio_context = ctx;
>> +}
>> +
>> /* Called with job_mutex *not* held. */
>> static void job_sleep_timer_cb(void *opaque)
>> {
>> @@ -1380,6 +1391,7 @@ int job_finish_sync_locked(Job *job,
>> {
>> Error *local_err = NULL;
>> int ret;
>> + assert(qemu_in_main_thread());
>> job_ref_locked(job);
>>
>
>
> Missed update of block_job_add_bdrv(), block_job_get_aio_context().
> Should they have an assertion too?
>
> Also some occurences in test, but that doesn't seem significant.
>
Both have GLOBAL_STATE_CODE.
Emanuele
