ratelimit: protect with a mutex

Right now, rate limiting is protected by the AioContext mutex, which is
taken for example both by the block jobs and by qmp_block_job_set_speed
(via find_block_job).

We would like to remove the dependency of block layer code on the
AioContext mutex, since most drivers and the core I/O code are already
not relying on it.  However, there is no existing lock that can easily
be taken by both ratelimit_set_speed and ratelimit_calculate_delay,
especially because the latter might run in coroutine context (and
therefore under a CoMutex) but the former will not.

Since concurrent calls to ratelimit_calculate_delay are not possible,
one idea could be to use a seqlock to get a snapshot of slice_ns and
slice_quota.  But for now keep it simple, and just add a mutex to the
RateLimit struct; block jobs are generally not performance critical to
the point of optimizing the clock cycles spent in synchronization.

This also requires the introduction of init/destroy functions, so
add them to the two users of ratelimit.h.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/blockjob.c b/blockjob.c
index 2fe1d788ba..dc1d9e0e46 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -87,6 +87,7 @@ void block_job_free(Job *job)
 
     block_job_remove_all_bdrv(bjob);
     blk_unref(bjob->blk);
+    ratelimit_destroy(&bjob->limit);
     error_free(bjob->blocker);
 }
 
@@ -442,6 +443,8 @@ void *block_job_create(const char *job_id, const BlockJobDriver *driver,
     assert(job->job.driver->free == &block_job_free);
     assert(job->job.driver->user_resume == &block_job_user_resume);
 
+    ratelimit_init(&job->limit);
+
     job->blk = blk;
 
     job->finalize_cancelled_notifier.notify = block_job_event_cancelled;