Re: [PATCH] block: don't deal with discard limit in blkdev_issue_discard()

[Ming Lei <ming.lei@redhat.com>]

On Fri, Oct 12, 2018 at 03:53:10PM +0800, Ming Lei wrote:
> blk_queue_split() does respect this limit via bio splitting, so no
> need to do that in blkdev_issue_discard(), then we can align to
> normal bio submit(bio_add_page() & submit_bio()).
> 
> More importantly, this patch fixes one issue introduced in a22c4d7e34402cc
> ("block: re-add discard_granularity and alignment checks"), in which
> zero discard bio may be generated in case of zero alignment.
> 
> Fixes: a22c4d7e34402ccdf3 ("block: re-add discard_granularity and alignment checks")
> Cc: stable@vger.kernel.org
> Cc: Mariusz Dabrowski <mariusz.dabrowski@intel.com>
> Cc: Ming Lin <ming.l@ssi.samsung.com>
> Cc: Mike Snitzer <snitzer@redhat.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Xiao Ni <xni@redhat.com>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
>  block/blk-lib.c | 28 ++--------------------------
>  1 file changed, 2 insertions(+), 26 deletions(-)
> 
> diff --git a/block/blk-lib.c b/block/blk-lib.c
> index d1b9dd03da25..bbd44666f2b5 100644
> --- a/block/blk-lib.c
> +++ b/block/blk-lib.c
> @@ -29,9 +29,7 @@ int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
>  {
>  	struct request_queue *q = bdev_get_queue(bdev);
>  	struct bio *bio = *biop;
> -	unsigned int granularity;
>  	unsigned int op;
> -	int alignment;
>  	sector_t bs_mask;
>  
>  	if (!q)
> @@ -54,38 +52,16 @@ int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
>  	if ((sector | nr_sects) & bs_mask)
>  		return -EINVAL;
>  
> -	/* Zero-sector (unknown) and one-sector granularities are the same.  */
> -	granularity = max(q->limits.discard_granularity >> 9, 1U);
> -	alignment = (bdev_discard_alignment(bdev) >> 9) % granularity;
> -
>  	while (nr_sects) {
> -		unsigned int req_sects;
> -		sector_t end_sect, tmp;
> +		unsigned int req_sects = nr_sects;
> +		sector_t end_sect;
>  
> -		/*
> -		 * Issue in chunks of the user defined max discard setting,
> -		 * ensuring that bi_size doesn't overflow
> -		 */
> -		req_sects = min_t(sector_t, nr_sects,
> -					q->limits.max_discard_sectors);
>  		if (!req_sects)
>  			goto fail;
>  		if (req_sects > UINT_MAX >> 9)
>  			req_sects = UINT_MAX >> 9;
>  
> -		/*
> -		 * If splitting a request, and the next starting sector would be
> -		 * misaligned, stop the discard at the previous aligned sector.
> -		 */
>  		end_sect = sector + req_sects;
> -		tmp = end_sect;
> -		if (req_sects < nr_sects &&
> -		    sector_div(tmp, granularity) != alignment) {
> -			end_sect = end_sect - alignment;
> -			sector_div(end_sect, granularity);
> -			end_sect = end_sect * granularity + alignment;
> -			req_sects = end_sect - sector;
> -		}
>  
>  		bio = next_bio(bio, 0, gfp_mask);
>  		bio->bi_iter.bi_sector = sector;
> -- 
> 2.9.5
> 

Ping...

This patch fixes BUG() in blk_mq_end_request() when zero-length discard
bio is generated from __blkdev_issue_discard().

Thanks,
Ming