From: Tejun Heo <tj@kernel.org>
Date: Mon, 5 Mar 2012 21:15:22 +0000 (-0800)
Subject: blkcg: drop unnecessary RCU locking
X-Git-Tag: v3.5-rc1~42^2~64
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c875f4d0250a1f070fa26087a73bdd8f54c48100;p=pandora-kernel.git

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>
---

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