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Re: [PATCH v10 14/21] jobs: protect job.aio_context with BQL and job_mut
From: |
Kevin Wolf |
Subject: |
Re: [PATCH v10 14/21] jobs: protect job.aio_context with BQL and job_mutex |
Date: |
Fri, 5 Aug 2022 11:12:10 +0200 |
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 <pbonzini@redhat.com>
> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
> Reviewed-by: Stefan Hajnoczi <stefanha@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.
> 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()?
> 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 */
I think this section comment should move down below aio_context now.
> - /** 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(),
Odd line break here in the middle of a sentence.
> + * 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 ecec66b44e..0a857b1468 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());
Same question about GLOBAL_STATE_CODE().
> + /* 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.
> + job->aio_context = ctx;
> +}
> +
> /* Called with job_mutex *not* held. */
> static void job_sleep_timer_cb(void *opaque)
> {
> @@ -1376,6 +1387,7 @@ int job_finish_sync_locked(Job *job,
> {
> Error *local_err = NULL;
> int ret;
> + assert(qemu_in_main_thread());
>
> job_ref_locked(job);
Another GLOBAL_STATE_CODE()?
Kevin
- Re: [PATCH v10 14/21] jobs: protect job.aio_context with BQL and job_mutex,
Kevin Wolf <=