2019-04-04 02:54:52

by Dongli Zhang

Subject: [PATCH 1/1] blk-mq: do not reset plug->rq_count before the list is sorted

We would never be able to sort the list if we first reset plug->rq_count
which is used in conditional check later.

Fixes: ce5b009cff19 ("block: improve logic around when to sort a plug list")
Signed-off-by: Dongli Zhang <[email protected]>
---
block/blk-mq.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 3ff3d7b..c162718 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1711,11 +1711,12 @@ void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
unsigned int depth;

list_splice_init(&plug->mq_list, &list);
- plug->rq_count = 0;

if (plug->rq_count > 2 && plug->multiple_queues)
list_sort(NULL, &list, plug_rq_cmp);

+ plug->rq_count = 0;
+
this_q = NULL;
this_hctx = NULL;
this_ctx = NULL;
--
2.7.4

2019-04-04 06:54:44

by Ming Lei

Subject: Re: [PATCH 1/1] blk-mq: do not reset plug->rq_count before the list is sorted

On Thu, Apr 4, 2019 at 10:54 AM Dongli Zhang <[email protected]> wrote:
>
> We would never be able to sort the list if we first reset plug->rq_count
> which is used in conditional check later.
>
> Fixes: ce5b009cff19 ("block: improve logic around when to sort a plug list")
> Signed-off-by: Dongli Zhang <[email protected]>
> ---
> block/blk-mq.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 3ff3d7b..c162718 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1711,11 +1711,12 @@ void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
> unsigned int depth;
>
> list_splice_init(&plug->mq_list, &list);
> - plug->rq_count = 0;
>
> if (plug->rq_count > 2 && plug->multiple_queues)
> list_sort(NULL, &list, plug_rq_cmp);
>
> + plug->rq_count = 0;
> +
> this_q = NULL;
> this_hctx = NULL;
> this_ctx = NULL;
> --
> 2.7.4
>

Reviewed-by: Ming Lei <[email protected]>

Thanks,
Ming Lei

2019-04-04 14:40:38

by Jens Axboe

Subject: Re: [PATCH 1/1] blk-mq: do not reset plug->rq_count before the list is sorted

On 4/3/19 8:57 PM, Dongli Zhang wrote:
> We would never be able to sort the list if we first reset plug->rq_count
> which is used in conditional check later.

Well, that was pretty stupid. Thanks for the patch, applied.

--
Jens Axboe