From 9f13ef678efd977487fc0c2e489f17c9a8c67a3e Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 5 Mar 2012 13:15:21 -0800 Subject: blkcg: use double locking instead of RCU for blkg synchronization blkgs are chained from both blkcgs and request_queues and thus subjected to two locks - blkcg->lock and q->queue_lock. As both blkcg and q can go away anytime, locking during removal is tricky. It's currently solved by wrapping removal inside RCU, which makes the synchronization complex. There are three locks to worry about - the outer RCU, q lock and blkcg lock, and it leads to nasty subtle complications like conditional synchronize_rcu() on queue exit paths. For all other paths, blkcg lock is naturally nested inside q lock and the only exception is blkcg removal path, which is a very cold path and can be implemented as clumsy but conceptually-simple reverse double lock dancing. This patch updates blkg removal path such that blkgs are removed while holding both q and blkcg locks, which is trivial for request queue exit path - blkg_destroy_all(). The blkcg removal path, blkiocg_pre_destroy(), implements reverse double lock dancing essentially identical to ioc_release_fn(). This simplifies blkg locking - no half-dead blkgs to worry about. Now unnecessary RCU annotations will be removed by the next patch. Signed-off-by: Tejun Heo Cc: Vivek Goyal Signed-off-by: Jens Axboe --- block/cfq.h | 10 ---------- 1 file changed, 10 deletions(-) (limited to 'block/cfq.h') diff --git a/block/cfq.h b/block/cfq.h index 5584e1b63ca8..c8b15ef57e5d 100644 --- a/block/cfq.h +++ b/block/cfq.h @@ -79,11 +79,6 @@ static inline void cfq_blkiocg_update_completion_stats(struct blkio_group *blkg, direction, sync); } -static inline int cfq_blkiocg_del_blkio_group(struct blkio_group *blkg) -{ - return blkiocg_del_blkio_group(blkg); -} - #else /* CFQ_GROUP_IOSCHED */ static inline void cfq_blkiocg_update_io_add_stats(struct blkio_group *blkg, struct blkio_policy_type *pol, @@ -119,10 +114,5 @@ static inline void cfq_blkiocg_update_completion_stats(struct blkio_group *blkg, struct blkio_policy_type *pol, uint64_t start_time, uint64_t io_start_time, bool direction, bool sync) { } -static inline int cfq_blkiocg_del_blkio_group(struct blkio_group *blkg) -{ - return 0; -} - #endif /* CFQ_GROUP_IOSCHED */ #endif -- cgit v1.2.3-59-g8ed1b