From 2a7f124414b35645049e9c1b125a6f0b470aa5ae Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@kernel.org>
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 <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
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 3699ab40d494..9beaac7fb397 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;
}
--
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