Messages in this thread | | | Date | Fri, 17 Feb 2012 11:19:58 -0500 | From | Vivek Goyal <> | Subject | Re: [PATCH 2/9] blkcg: drop unnecessary RCU locking |
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On Thu, Feb 16, 2012 at 02:37:51PM -0800, Tejun Heo wrote: > Now that blkg additions / removals are always done under both q and > blkcg locks, the only place RCU locking is used is blkg_lookup() for > lockless lookup. This patch drops unncessary RCU locking replacing it > with plain blkcg / q locking as necessary. > > * blkg_lookup_create() and blkiocg_pre_destroy() already perform > proper locking and don't need RCU. Dropped.
But blkg_lookup_create() is called under rcu() to protect blkcg pointer. And blkg_lookup() is also happening under same rcu read lock. So I think you can't drop rcu from blkg_lookup_create().
> { > struct blkio_group *blkg, *new_blkg; > > - WARN_ON_ONCE(!rcu_read_lock_held());
Don't we want to be called with rcu lock held needed for blkg_lookup()?
> lockdep_assert_held(q->queue_lock); > > /*
[..] > @@ -581,11 +580,9 @@ struct blkio_group *blkg_lookup_create(struct blkio_cgroup *blkcg, > * allocation is fixed. > */ > spin_unlock_irq(q->queue_lock); > - rcu_read_unlock(); > > new_blkg = blkg_alloc(blkcg, q); > > - rcu_read_lock(); > spin_lock_irq(q->queue_lock);
blkg_alloc() might sleep here with rcu lock held?
Thanks Vivek
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