From 2a7f124414b35645049e9c1b125a6f0b470aa5ae Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 5 Mar 2012 13:15:01 -0800 Subject: blkcg: move rcu_read_lock() outside of blkio_group get functions rcu_read_lock() in throtl_get_tb() and cfq_get_cfqg() holds onto @blkcg while looking up blkg. For API cleanup, the next patch will make the caller responsible for determining @blkcg to look blkg from and let them specify it as a parameter. Move rcu read locking out to the callers to prepare for the change. -v2: Originally this patch was described as a fix for RCU read locking bug around @blkg, which Vivek pointed out to be incorrect. It was from misunderstanding the role of rcu locking as protecting @blkg not @blkcg. Patch description updated. Signed-off-by: Tejun Heo Cc: Vivek Goyal Signed-off-by: Jens Axboe --- block/blk-throttle.c | 18 ++++++------------ 1 file changed, 6 insertions(+), 12 deletions(-) (limited to 'block/blk-throttle.c') diff --git a/block/blk-throttle.c b/block/blk-throttle.c index 3699ab40d49..9beaac7fb39 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -313,25 +313,23 @@ static struct throtl_grp * throtl_get_tg(struct throtl_data *td) if (unlikely(blk_queue_bypass(q))) return NULL; - rcu_read_lock(); blkcg = task_blkio_cgroup(current); tg = throtl_find_tg(td, blkcg); - if (tg) { - rcu_read_unlock(); + if (tg) return tg; - } /* * Need to allocate a group. Allocation of group also needs allocation * of per cpu stats which in-turn takes a mutex() and can block. Hence * we need to drop rcu lock and queue_lock before we call alloc. */ - rcu_read_unlock(); spin_unlock_irq(q->queue_lock); + rcu_read_unlock(); tg = throtl_alloc_tg(td); /* Group allocated and queue is still alive. take the lock */ + rcu_read_lock(); spin_lock_irq(q->queue_lock); /* Make sure @q is still alive */ @@ -343,7 +341,6 @@ static struct throtl_grp * throtl_get_tg(struct throtl_data *td) /* * Initialize the new group. After sleeping, read the blkcg again. */ - rcu_read_lock(); blkcg = task_blkio_cgroup(current); /* @@ -354,7 +351,6 @@ static struct throtl_grp * throtl_get_tg(struct throtl_data *td) if (__tg) { kfree(tg); - rcu_read_unlock(); return __tg; } @@ -365,7 +361,6 @@ static struct throtl_grp * throtl_get_tg(struct throtl_data *td) } throtl_init_add_tg_lists(td, tg, blkcg); - rcu_read_unlock(); return tg; } @@ -1150,7 +1145,6 @@ bool blk_throtl_bio(struct request_queue *q, struct bio *bio) * basic fields like stats and io rates. If a group has no rules, * just update the dispatch stats in lockless manner and return. */ - rcu_read_lock(); blkcg = task_blkio_cgroup(current); tg = throtl_find_tg(td, blkcg); @@ -1160,11 +1154,9 @@ bool blk_throtl_bio(struct request_queue *q, struct bio *bio) if (tg_no_rule_group(tg, rw)) { blkiocg_update_dispatch_stats(&tg->blkg, bio->bi_size, rw, rw_is_sync(bio->bi_rw)); - rcu_read_unlock(); - goto out; + goto out_unlock_rcu; } } - rcu_read_unlock(); /* * Either group has not been allocated yet or it is not an unlimited @@ -1222,6 +1214,8 @@ queue_bio: out_unlock: spin_unlock_irq(q->queue_lock); +out_unlock_rcu: + rcu_read_unlock(); out: return throttled; } -- cgit v1.2.3