Re: [PATCH 5.16 1026/1039] blk-mq: fix tag_get wait task cant be awakened

[John Garry]

On 24/01/2022 18:46, Greg Kroah-Hartman wrote:
> From: Laibin Qiu<qiulaibin@xxxxxxxxxx>
>
> commit 180dccb0dba4f5e84a4a70c1be1d34cbb6528b32 upstream.
>
> In case of shared tags, there might be more than one hctx which
> allocates from the same tags, and each hctx is limited to allocate at
> most:
>          hctx_max_depth = max((bt->sb.depth + users - 1) / users, 4U);
>
> tag idle detection is lazy, and may be delayed for 30sec, so there
> could be just one real active hctx(queue) but all others are actually
> idle and still accounted as active because of the lazy idle detection.
> Then if wake_batch is > hctx_max_depth, driver tag allocation may wait
> forever on this real active hctx.
>
> Fix this by recalculating wake_batch when inc or dec active_queues.
>
> Fixes: 0d2602ca30e41 ("blk-mq: improve support for shared tags maps")
> Suggested-by: Ming Lei<ming.lei@xxxxxxxxxx>
> Suggested-by: John Garry<john.garry@xxxxxxxxxx>
> Signed-off-by: Laibin Qiu<qiulaibin@xxxxxxxxxx>
> Reviewed-by: Andy Shevchenko<andriy.shevchenko@xxxxxxxxxxxxxxx>
> Link:https://lore.kernel.org/r/20220113025536.1479653-1-qiulaibin@xxxxxxxxxx
> Signed-off-by: Jens Axboe<axboe@xxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman<gregkh@xxxxxxxxxxxxxxxxxxx>

JFYI, Somebody reported a hang with this commit:
https://lore.kernel.org/linux-block/78cafe94-a787-e006-8851-69906f0c2128@xxxxxxxxxx/T/#t

Thanks,
John