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    Subject[PATCH 5.9 662/757] blk-mq: always allow reserved allocation in hctx_may_queue
    Date
    From: Ming Lei <ming.lei@redhat.com>

    [ Upstream commit 285008501c65a3fcee05d2c2c26cbf629ceff2f0 ]

    NVMe shares tagset between fabric queue and admin queue or between
    connect_q and NS queue, so hctx_may_queue() can be called to allocate
    request for these queues.

    Tags can be reserved in these tagset. Before error recovery, there is
    often lots of in-flight requests which can't be completed, and new
    reserved request may be needed in error recovery path. However,
    hctx_may_queue() can always return false because there is too many
    in-flight requests which can't be completed during error handling.
    Finally, nothing can proceed.

    Fix this issue by always allowing reserved tag allocation in
    hctx_may_queue(). This is reasonable because reserved tags are supposed
    to always be available.

    Reviewed-by: Christoph Hellwig <hch@lst.de>
    Reviewed-by: Hannes Reinecke <hare@suse.de>
    Cc: David Milburn <dmilburn@redhat.com>
    Cc: Ewan D. Milne <emilne@redhat.com>
    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-tag.c | 3 ++-
    block/blk-mq.c | 5 +++--
    2 files changed, 5 insertions(+), 3 deletions(-)

    diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
    index 32d82e23b0953..a1c1e7c611f7b 100644
    --- a/block/blk-mq-tag.c
    +++ b/block/blk-mq-tag.c
    @@ -59,7 +59,8 @@ void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
    static int __blk_mq_get_tag(struct blk_mq_alloc_data *data,
    struct sbitmap_queue *bt)
    {
    - if (!data->q->elevator && !hctx_may_queue(data->hctx, bt))
    + if (!data->q->elevator && !(data->flags & BLK_MQ_REQ_RESERVED) &&
    + !hctx_may_queue(data->hctx, bt))
    return BLK_MQ_NO_TAG;

    if (data->shallow_depth)
    diff --git a/block/blk-mq.c b/block/blk-mq.c
    index c27a61029cdd0..94a53d779c12b 100644
    --- a/block/blk-mq.c
    +++ b/block/blk-mq.c
    @@ -1105,10 +1105,11 @@ static bool __blk_mq_get_driver_tag(struct request *rq)
    if (blk_mq_tag_is_reserved(rq->mq_hctx->sched_tags, rq->internal_tag)) {
    bt = &rq->mq_hctx->tags->breserved_tags;
    tag_offset = 0;
    + } else {
    + if (!hctx_may_queue(rq->mq_hctx, bt))
    + return false;
    }

    - if (!hctx_may_queue(rq->mq_hctx, bt))
    - return false;
    tag = __sbitmap_queue_get(bt);
    if (tag == BLK_MQ_NO_TAG)
    return false;
    --
    2.25.1


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