On Mon, Jan 22, 2018 at 11:35:49AM +0800, Ming Lei wrote:
> DM-MPATH need to allocate request from underlying queue, but when the
> allocation fails, there is no way to make underlying queue's RESTART
> to restart DM's queue.
>
> This patch introduces blk_get_request_notify() for this purpose, and
> caller need to pass 'wait_queue_entry_t' to this function, and make
> sure it is initialized well, so after the current allocation fails,
> DM will get notified when there is request available from underlying
> queue.
>
> This approach is suggested by Jens, and has been used in blk-mq dispatch
> patch for a while, see blk_mq_mark_tag_wait().
>
> Suggested-by: Jens Axboe <axboe@xxxxxxxxx>
> Cc: Mike Snitzer <snitzer@xxxxxxxxxx>
> Cc: Laurence Oberman <loberman@xxxxxxxxxx>
> Cc: Bart Van Assche <bart.vanassche@xxxxxxxxxxx>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
> block/blk-mq-tag.c | 27 ++++++++++++++++++++++++++-
> block/blk-mq.c | 24 +++++++++++++++++++++---
> block/blk-mq.h | 1 +
> include/linux/blk-mq.h | 5 +++++
> 4 files changed, 53 insertions(+), 4 deletions(-)
>
> diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
> index 336dde07b230..911fc9bd1bab 100644
> --- a/block/blk-mq-tag.c
> +++ b/block/blk-mq-tag.c
> @@ -128,10 +128,35 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
> if (tag != -1)
> goto found_tag;
>
> - if (data->flags & BLK_MQ_REQ_NOWAIT)
> + if ((data->flags & BLK_MQ_REQ_NOWAIT) && !(data->notifier &&
> + (data->flags & BLK_MQ_REQ_ALLOC_NOTIFY)))
> return BLK_MQ_TAG_FAIL;
>
> ws = bt_wait_ptr(bt, data->hctx);
> +
> + /*
> + * If caller requires notification when tag is available, add
> + * wait entry of 'data->notifier' to the wait queue.
> + */
> + if (data->flags & BLK_MQ_REQ_NOWAIT) {
> + bool added = false;
> +
> + spin_lock_irq(&ws->wait.lock);
> + if (list_empty(&data->notifier->entry))
> + __add_wait_queue(&ws->wait, data->notifier);
> + else
> + added = true;
> + spin_unlock_irq(&ws->wait.lock);
The above need a per-notifier lock too, since the same notifier may
be added to different wait queues at the same time.
--
Ming
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