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    Subject[PATCH 5.3 196/197] blk-rq-qos: fix first node deletion of rq_qos_del()
    Date
    From: Tejun Heo <tj@kernel.org>

    commit 307f4065b9d7c1e887e8bdfb2487e4638559fea1 upstream.

    rq_qos_del() incorrectly assigns the node being deleted to the head if
    it was the first on the list in the !prev path. Fix it by iterating
    with ** instead.

    Signed-off-by: Tejun Heo <tj@kernel.org>
    Cc: Josef Bacik <josef@toxicpanda.com>
    Fixes: a79050434b45 ("blk-rq-qos: refactor out common elements of blk-wbt")
    Cc: stable@vger.kernel.org # v4.19+
    Signed-off-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    block/blk-rq-qos.h | 13 +++++--------
    1 file changed, 5 insertions(+), 8 deletions(-)

    --- a/block/blk-rq-qos.h
    +++ b/block/blk-rq-qos.h
    @@ -103,16 +103,13 @@ static inline void rq_qos_add(struct req

    static inline void rq_qos_del(struct request_queue *q, struct rq_qos *rqos)
    {
    - struct rq_qos *cur, *prev = NULL;
    - for (cur = q->rq_qos; cur; cur = cur->next) {
    - if (cur == rqos) {
    - if (prev)
    - prev->next = rqos->next;
    - else
    - q->rq_qos = cur;
    + struct rq_qos **cur;
    +
    + for (cur = &q->rq_qos; *cur; cur = &(*cur)->next) {
    + if (*cur == rqos) {
    + *cur = rqos->next;
    break;
    }
    - prev = cur;
    }

    blk_mq_debugfs_unregister_rqos(rqos);

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