diff options
author | Tejun Heo <tj@kernel.org> | 2012-04-13 23:50:53 +0200 |
---|---|---|
committer | Jens Axboe <axboe@kernel.dk> | 2012-04-20 10:06:06 +0200 |
commit | 80fd99792b0b9f162abdf3da12fb10eb9eb5f321 (patch) | |
tree | 3273581c76d9bcad18f0668f6707be9323e650fb /block/blk-core.c | |
parent | blkcg: make blkg_conf_prep() take @pol and return with queue lock held (diff) | |
download | linux-80fd99792b0b9f162abdf3da12fb10eb9eb5f321.tar.xz linux-80fd99792b0b9f162abdf3da12fb10eb9eb5f321.zip |
blkcg: make sure blkg_lookup() returns %NULL if @q is bypassing
Currently, blkg_lookup() doesn't check @q bypass state. This patch
updates blk_queue_bypass_start() to do synchronize_rcu() before
returning and updates blkg_lookup() to check blk_queue_bypass() and
return %NULL if bypassing. This ensures blkg_lookup() returns %NULL
if @q is bypassing.
This is to guarantee that nobody is accessing policy data while @q is
bypassing, which is necessary to allow replacing blkio_cgroup->pd[] in
place on policy [de]activation.
v2: Added more comments explaining bypass guarantees as suggested by
Vivek.
v3: Added more comments explaining why there's no synchronize_rcu() in
blk_cleanup_queue() as suggested by Vivek.
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-core.c')
-rw-r--r-- | block/blk-core.c | 15 |
1 files changed, 13 insertions, 2 deletions
diff --git a/block/blk-core.c b/block/blk-core.c index 991c1d6ef245..f2db628aa509 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -416,7 +416,8 @@ void blk_drain_queue(struct request_queue *q, bool drain_all) * In bypass mode, only the dispatch FIFO queue of @q is used. This * function makes @q enter bypass mode and drains all requests which were * throttled or issued before. On return, it's guaranteed that no request - * is being throttled or has ELVPRIV set. + * is being throttled or has ELVPRIV set and blk_queue_bypass() %true + * inside queue or RCU read lock. */ void blk_queue_bypass_start(struct request_queue *q) { @@ -426,6 +427,8 @@ void blk_queue_bypass_start(struct request_queue *q) spin_unlock_irq(q->queue_lock); blk_drain_queue(q, false); + /* ensure blk_queue_bypass() is %true inside RCU read lock */ + synchronize_rcu(); } EXPORT_SYMBOL_GPL(blk_queue_bypass_start); @@ -462,7 +465,15 @@ void blk_cleanup_queue(struct request_queue *q) spin_lock_irq(lock); - /* dead queue is permanently in bypass mode till released */ + /* + * Dead queue is permanently in bypass mode till released. Note + * that, unlike blk_queue_bypass_start(), we aren't performing + * synchronize_rcu() after entering bypass mode to avoid the delay + * as some drivers create and destroy a lot of queues while + * probing. This is still safe because blk_release_queue() will be + * called only after the queue refcnt drops to zero and nothing, + * RCU or not, would be traversing the queue by then. + */ q->bypass_depth++; queue_flag_set(QUEUE_FLAG_BYPASS, q); |