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    Subject[PATCH 4.14 028/189] blkcg: dont hold blkcg lock when deactivating policy
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

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

    From: Jiang Biao <jiang.biao2@zte.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@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>
    ---
    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);

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