linux-kernel - [PATCH 4.14 028/189] blkcg: dont hold blkcg lock when deactivating policy

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Message-Id: <20180618081210.419522594@linuxfoundation.org>
Date:   Mon, 18 Jun 2018 10:12:04 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jiang Biao <jiang.biao2@....com.cn>,
        Wen Yang <wen.yang99@....com.cn>, Tejun Heo <tj@...nel.org>,
        Jens Axboe <axboe@...nel.dk>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: [PATCH 4.14 028/189] blkcg: dont hold blkcg lock when deactivating policy

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jiang Biao <jiang.biao2@....com.cn>

[ 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@....com.cn>
Signed-off-by: Wen Yang <wen.yang99@....com.cn>
CC: Tejun Heo <tj@...nel.org>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 block/blk-cgroup.c |    5 -----
 1 file changed, 5 deletions(-)

--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1374,17 +1374,12 @@ void blkcg_deactivate_policy(struct requ
 	__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);