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    Subject[PATCH AUTOSEL 5.0 66/79] blk-mq: introduce blk_mq_complete_request_sync()
    Date
    From: Ming Lei <ming.lei@redhat.com>

    [ Upstream commit 1b8f21b74c3c9c82fce5a751d7aefb7cc0b8d33d ]

    In NVMe's error handler, follows the typical steps of tearing down
    hardware for recovering controller:

    1) stop blk_mq hw queues
    2) stop the real hw queues
    3) cancel in-flight requests via
    blk_mq_tagset_busy_iter(tags, cancel_request, ...)
    cancel_request():
    mark the request as abort
    blk_mq_complete_request(req);
    4) destroy real hw queues

    However, there may be race between #3 and #4, because blk_mq_complete_request()
    may run q->mq_ops->complete(rq) remotelly and asynchronously, and
    ->complete(rq) may be run after #4.

    This patch introduces blk_mq_complete_request_sync() for fixing the
    above race.

    Cc: Sagi Grimberg <sagi@grimberg.me>
    Cc: Bart Van Assche <bvanassche@acm.org>
    Cc: James Smart <james.smart@broadcom.com>
    Cc: linux-nvme@lists.infradead.org
    Reviewed-by: Keith Busch <keith.busch@intel.com>
    Reviewed-by: Christoph Hellwig <hch@lst.de>
    Signed-off-by: Ming Lei <ming.lei@redhat.com>
    Signed-off-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    block/blk-mq.c | 7 +++++++
    include/linux/blk-mq.h | 1 +
    2 files changed, 8 insertions(+)

    diff --git a/block/blk-mq.c b/block/blk-mq.c
    index 16f9675c57e6..ce462c313806 100644
    --- a/block/blk-mq.c
    +++ b/block/blk-mq.c
    @@ -657,6 +657,13 @@ bool blk_mq_complete_request(struct request *rq)
    }
    EXPORT_SYMBOL(blk_mq_complete_request);

    +void blk_mq_complete_request_sync(struct request *rq)
    +{
    + WRITE_ONCE(rq->state, MQ_RQ_COMPLETE);
    + rq->q->mq_ops->complete(rq);
    +}
    +EXPORT_SYMBOL_GPL(blk_mq_complete_request_sync);
    +
    int blk_mq_request_started(struct request *rq)
    {
    return blk_mq_rq_state(rq) != MQ_RQ_IDLE;
    diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
    index 0e030f5f76b6..7e092bdac27f 100644
    --- a/include/linux/blk-mq.h
    +++ b/include/linux/blk-mq.h
    @@ -306,6 +306,7 @@ void blk_mq_add_to_requeue_list(struct request *rq, bool at_head,
    void blk_mq_kick_requeue_list(struct request_queue *q);
    void blk_mq_delay_kick_requeue_list(struct request_queue *q, unsigned long msecs);
    bool blk_mq_complete_request(struct request *rq);
    +void blk_mq_complete_request_sync(struct request *rq);
    bool blk_mq_bio_list_merge(struct request_queue *q, struct list_head *list,
    struct bio *bio);
    bool blk_mq_queue_stopped(struct request_queue *q);
    --
    2.19.1
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