blkcg: don't hold blkcg lock when deactivating policy

BugLink: http://bugs.launchpad.net/bugs/1794889
[ Upstream commit 946b81da114b8ba5c74bb01e57c0c6eca2bdc801 ]

As described in the comment of blkcg_activate_policy(),
*Update of each blkg is protected by both queue and blkcg locks so
that holding either lock and testing blkcg_policy_enabled() is
always enough for dereferencing policy data.*
with queue lock held, there is no need to hold blkcg lock in
blkcg_deactivate_policy(). Similar case is in
blkcg_activate_policy(), which has removed holding of blkcg lock in
commit 4c55f4f9ad3001ac1fefdd8d8ca7641d18558e23.

Signed-off-by: Jiang Biao <jiang.biao2@zte.com.cn>
Signed-off-by: Wen Yang <wen.yang99@zte.com.cn>
CC: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 4117524ca45bc76cceb163c42f752ffd8d7e1659..0bc4b8ac9f659ac842ffeb3a0b28c2fbfe65b138 100644 (file)
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1374,17 +1374,12 @@ void blkcg_deactivate_policy(struct request_queue *q,
        __clear_bit(pol->plid, q->blkcg_pols);
 
        list_for_each_entry(blkg, &q->blkg_list, q_node) {
-               /* grab blkcg lock too while removing @pd from @blkg */
-               spin_lock(&blkg->blkcg->lock);
-
                if (blkg->pd[pol->plid]) {
                        if (pol->pd_offline_fn)
                                pol->pd_offline_fn(blkg->pd[pol->plid]);
                        pol->pd_free_fn(blkg->pd[pol->plid]);
                        blkg->pd[pol->plid] = NULL;
                }
-
-               spin_unlock(&blkg->blkcg->lock);
        }
 
        spin_unlock_irq(q->queue_lock);