On Sat, May 19, 2018 at 03:44:06PM +0800, Ming Lei wrote:
> When the allocation process is scheduled back and the mapped hw queue is
> changed, do one extra wake up on orignal queue for compensating wake up
> miss, so other allocations on the orignal queue won't be starved.
>
> This patch fixes one request allocation hang issue, which can be
> triggered easily in case of very low nr_request.
>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Cc: Omar Sandoval <osandov@xxxxxx>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
>
> V2:
> fix build failure
>
> block/blk-mq-tag.c | 13 +++++++++++++
> include/linux/sbitmap.h | 7 +++++++
> lib/sbitmap.c | 6 ++++++
> 3 files changed, 26 insertions(+)
>
> diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
> index 336dde07b230..77607f89d205 100644
> --- a/block/blk-mq-tag.c
> +++ b/block/blk-mq-tag.c
> @@ -134,6 +134,8 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
> ws = bt_wait_ptr(bt, data->hctx);
> drop_ctx = data->ctx == NULL;
> do {
> + struct sbitmap_queue *bt_orig;
> +
> /*
> * We're out of tags on this hardware queue, kick any
> * pending IO submits before going to sleep waiting for
> @@ -159,6 +161,7 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
> if (data->ctx)
> blk_mq_put_ctx(data->ctx);
>
> + bt_orig = bt;
> io_schedule();
>
> data->ctx = blk_mq_get_ctx(data->q);
> @@ -170,6 +173,16 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
> bt = &tags->bitmap_tags;
>
> finish_wait(&ws->wait, &wait);
> +
> + /*
> + * If destination hw queue is changed, wake up original
> + * queue one extra time for compensating the wake up
> + * miss, so other allocations on original queue won't
> + * be starved.
> + */
> + if (bt != bt_orig)
> + sbitmap_queue_wake_up(bt_orig);
> +
> ws = bt_wait_ptr(bt, data->hctx);
> } while (1);
>
> diff --git a/include/linux/sbitmap.h b/include/linux/sbitmap.h
> index 841585f6e5f2..b23f50355281 100644
> --- a/include/linux/sbitmap.h
> +++ b/include/linux/sbitmap.h
> @@ -484,6 +484,13 @@ static inline struct sbq_wait_state *sbq_wait_ptr(struct sbitmap_queue *sbq,
> void sbitmap_queue_wake_all(struct sbitmap_queue *sbq);
>
> /**
> + * sbitmap_wake_up() - Do a regular wake up compensation if the queue
> + * allocated from is changed after scheduling back.
> + * @sbq: Bitmap queue to wake up.
> + */
> +void sbitmap_queue_wake_up(struct sbitmap_queue *sbq);
> +
> +/**
> * sbitmap_queue_show() - Dump &struct sbitmap_queue information to a &struct
> * seq_file.
> * @sbq: Bitmap queue to show.
> diff --git a/lib/sbitmap.c b/lib/sbitmap.c
> index e6a9c06ec70c..c6ae4206bcb1 100644
> --- a/lib/sbitmap.c
> +++ b/lib/sbitmap.c
> @@ -466,6 +466,12 @@ static void sbq_wake_up(struct sbitmap_queue *sbq)
> }
> }
>
> +void sbitmap_queue_wake_up(struct sbitmap_queue *sbq)
> +{
> + sbq_wake_up(sbq);
> +}
> +EXPORT_SYMBOL_GPL(sbitmap_queue_wake_up);
There's no reason to wrap an internal helper with a function taking the
same arguments, just rename sbq_wake_up() and export it.
