Re: [PATCH 1/4] block: break discard submissions into the user defined size

[Omar Sandoval <osandov@osandov.com>]

On Mon, May 07, 2018 at 10:13:32AM -0600, Jens Axboe wrote:
> Don't build discards bigger than what the user asked for, if the
> user decided to limit the size by writing to 'discard_max_bytes'.
> 
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> ---
>  block/blk-lib.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/block/blk-lib.c b/block/blk-lib.c
> index a676084d4740..7417d617091b 100644
> --- a/block/blk-lib.c
> +++ b/block/blk-lib.c
> @@ -62,10 +62,11 @@ int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
>  		unsigned int req_sects;
>  		sector_t end_sect, tmp;
>  
> -		/* Make sure bi_size doesn't overflow */
> -		req_sects = min_t(sector_t, nr_sects, UINT_MAX >> 9);
> +		/* Issue in chunks of the user defined max discard setting */
> +		req_sects = min_t(sector_t, nr_sects,
> +					q->limits.max_discard_sectors);
>  

Some drivers, including nvme, do

   blk_queue_max_discard_sectors(q, UINT_MAX)

That means q->limits.max_discard_sectors can be UINT_MAX, and

    bio->bi_iter.bi_size = req_sects << 9;

will overflow. We should probably cap max_discard_sectors at
UINT_MAX >> 9 in a prep patch.