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| author | Tejun Heo <tj@kernel.org> | 2012-03-05 13:15:21 -0800 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2012-03-06 21:27:24 +0100 |
| commit | 9f13ef678efd977487fc0c2e489f17c9a8c67a3e (patch) | |
| tree | e58a2dd153ad24b2ea173d5dfb575c507e1f7589 /block/blk-cgroup.h | |
| parent | e8989fae38d9831c72b20375a206a919ca468c52 (diff) | |
| download | linux-9f13ef678efd977487fc0c2e489f17c9a8c67a3e.tar.gz linux-9f13ef678efd977487fc0c2e489f17c9a8c67a3e.tar.bz2 linux-9f13ef678efd977487fc0c2e489f17c9a8c67a3e.zip | |
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 <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/blk-cgroup.h')
| -rw-r--r-- | block/blk-cgroup.h | 4 |
1 files changed, 0 insertions, 4 deletions
diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h index 6e8ee86a2870..df73040a6a5f 100644 --- a/block/blk-cgroup.h +++ b/block/blk-cgroup.h @@ -380,7 +380,6 @@ static inline void blkiocg_set_start_empty_time(struct blkio_group *blkg, extern struct blkio_cgroup blkio_root_cgroup; extern struct blkio_cgroup *cgroup_to_blkio_cgroup(struct cgroup *cgroup); extern struct blkio_cgroup *task_blkio_cgroup(struct task_struct *tsk); -extern int blkiocg_del_blkio_group(struct blkio_group *blkg); extern struct blkio_group *blkg_lookup(struct blkio_cgroup *blkcg, struct request_queue *q); struct blkio_group *blkg_lookup_create(struct blkio_cgroup *blkcg, @@ -416,9 +415,6 @@ cgroup_to_blkio_cgroup(struct cgroup *cgroup) { return NULL; } static inline struct blkio_cgroup * task_blkio_cgroup(struct task_struct *tsk) { return NULL; } -static inline int -blkiocg_del_blkio_group(struct blkio_group *blkg) { return 0; } - static inline struct blkio_group *blkg_lookup(struct blkio_cgroup *blkcg, void *key) { return NULL; } static inline void blkiocg_update_timeslice_used(struct blkio_group *blkg, |