Re: [PATCH] block: fix blk_queue_end_tag()

From: Tao Ma
Date: Wed Dec 21 2011 - 01:33:44 EST


On 12/21/2011 07:33 AM, Dan Williams wrote:
> Commit 5e081591 "block: warn if tag is greater than real_max_depth"
> cleaned up blk_queue_end_tag() to warn when the tag is truly invalid
> (greater than real_max_depth). However, it changed behavior in the tag
> < max_depth case to not end the request. Leading to triggering of
> BUG_ON(blk_queued_rq(rq)) in the request completion path:
>
> http://marc.info/?l=linux-kernel&m=132204370518629&w=2
>
> In order to allow blk_queue_resize_tags() to shrink the tag space
> blk_queue_end_tag() must always complete tags with a value less than
> real_max_depth regardless of the current max_depth.
>
> Cc: Tao Ma <boyu.mt@xxxxxxxxxx>
> Reported-by: Meelis Roos <mroos@xxxxx>
> Reported-by: Ed Nadolski <edmund.nadolski@xxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> ---
> Functionally the same as Tao Ma's fix [1], but just moves the warn into the
> if() directly.
>
> [1]: http://marc.info/?l=linux-scsi&m=132439698602441&w=2
>
> --
> Dan
>
> block/blk-tag.c | 5 +++--
> 1 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/block/blk-tag.c b/block/blk-tag.c
> index e74d6d1..6e61262 100644
> --- a/block/blk-tag.c
> +++ b/block/blk-tag.c
> @@ -286,12 +286,13 @@ void blk_queue_end_tag(struct request_queue *q, struct request *rq)
>
> BUG_ON(tag == -1);
>
> - if (unlikely(tag >= bqt->max_depth)) {
> + if (WARN_ONCE(tag >= bqt->real_max_depth,
> + "%s: tag %d greater than tag map size: %d\n",
> + __func__, tag, bqt->real_max_depth)) {
> /*
> * This can happen after tag depth has been reduced.
Please also change the comments here since it should never happen in the
right workload.

Thanks
Tao
> * But tag shouldn't be larger than real_max_depth.
> */
> - WARN_ON(tag >= bqt->real_max_depth);
> return;
> }
>
>
> --
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