blkcg: drop unnecessary RCU locking
Now that blkg additions / removals are always done under both q and
blkcg locks, the only places RCU locking is necessary are
blkg_lookup[_create]() for lookup w/o blkcg lock. This patch drops
unncessary RCU locking replacing it with plain blkcg locking as
necessary.
* blkiocg_pre_destroy() already perform proper locking and don't need
RCU. Dropped.
* blkio_read_blkg_stats() now uses blkcg->lock instead of RCU read
lock. This isn't a hot path.
* Now unnecessary synchronize_rcu() from queue exit paths removed.
This makes q->nr_blkgs unnecessary. Dropped.
* RCU annotation on blkg->q removed.
-v2: Vivek pointed out that blkg_lookup_create() still needs to be
called under rcu_read_lock(). Updated.
-v3: After the update, stats_lock locking in blkio_read_blkg_stats()
shouldn't be using _irq variant as it otherwise ends up enabling
irq while blkcg->lock is locked. Fixed.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index e35ee7a..bfa5168 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -1046,39 +1046,8 @@
void blk_throtl_exit(struct request_queue *q)
{
- struct throtl_data *td = q->td;
- bool wait;
-
- BUG_ON(!td);
-
+ BUG_ON(!q->td);
throtl_shutdown_wq(q);
-
- /* If there are other groups */
- spin_lock_irq(q->queue_lock);
- wait = q->nr_blkgs;
- spin_unlock_irq(q->queue_lock);
-
- /*
- * Wait for tg_to_blkg(tg)->q accessors to exit their grace periods.
- * Do this wait only if there are other undestroyed groups out
- * there (other than root group). This can happen if cgroup deletion
- * path claimed the responsibility of cleaning up a group before
- * queue cleanup code get to the group.
- *
- * Do not call synchronize_rcu() unconditionally as there are drivers
- * which create/delete request queue hundreds of times during scan/boot
- * and synchronize_rcu() can take significant time and slow down boot.
- */
- if (wait)
- synchronize_rcu();
-
- /*
- * Just being safe to make sure after previous flush if some body did
- * update limits through cgroup and another work got queued, cancel
- * it.
- */
- throtl_shutdown_wq(q);
-
kfree(q->td);
}