linux-kernel - Re: [PATCH V2 2/5] dm: ignore discard return value

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Message-Id: <d86b820a-46c9-43b6-9fe2-dbd991b76520@fnnas.com>
Date: Mon, 24 Nov 2025 14:24:05 +0800
From: "Yu Kuai" <yukuai@...as.com>
To: "Chaitanya Kulkarni" <ckulkarnilinux@...il.com>, <axboe@...nel.dk>, 
	<agk@...hat.com>, <snitzer@...nel.org>, <mpatocka@...hat.com>, 
	<song@...nel.org>, <hch@....de>, <sagi@...mberg.me>, <kch@...dia.com>, 
	<jaegeuk@...nel.org>, <chao@...nel.org>, <cem@...nel.org>, 
	"Yu Kuai" <yukuai@...as.com>
Cc: <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>, 
	<dm-devel@...ts.linux.dev>, <linux-raid@...r.kernel.org>, 
	<linux-nvme@...ts.infradead.org>, 
	<linux-f2fs-devel@...ts.sourceforge.net>, <linux-xfs@...r.kernel.org>, 
	<bpf@...r.kernel.org>
Subject: Re: [PATCH V2 2/5] dm: ignore discard return value

Hi,

在 2025/11/24 10:57, Chaitanya Kulkarni 写道:
> __blkdev_issue_discard() always returns 0, making all error checking
> at call sites dead code.
>
> For dm-thin change issue_discard() return type to void, in
> passdown_double_checking_shared_status() remove the r assignment from
> return value of the issue_discard(), for end_discard() hardcod value
> of r to 0 that matches only value returned from
> __blkdev_issue_discard().
>
> md part is simplified to only check !discard_bio by ignoring the
> __blkdev_issue_discard() value.
>
> Signed-off-by: Chaitanya Kulkarni <ckulkarnilinux@...il.com>
> ---
>   drivers/md/dm-thin.c | 12 +++++-------
>   drivers/md/md.c      |  4 ++--
>   2 files changed, 7 insertions(+), 9 deletions(-)

mdraid and dm are different drivers, please split them.

>
> diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
> index c84149ba4e38..77c76f75c85f 100644
> --- a/drivers/md/dm-thin.c
> +++ b/drivers/md/dm-thin.c
> @@ -395,13 +395,13 @@ static void begin_discard(struct discard_op *op, struct thin_c *tc, struct bio *
>   	op->bio = NULL;
>   }
>   
> -static int issue_discard(struct discard_op *op, dm_block_t data_b, dm_block_t data_e)
> +static void issue_discard(struct discard_op *op, dm_block_t data_b, dm_block_t data_e)
>   {
>   	struct thin_c *tc = op->tc;
>   	sector_t s = block_to_sectors(tc->pool, data_b);
>   	sector_t len = block_to_sectors(tc->pool, data_e - data_b);
>   
> -	return __blkdev_issue_discard(tc->pool_dev->bdev, s, len, GFP_NOIO, &op->bio);
> +	__blkdev_issue_discard(tc->pool_dev->bdev, s, len, GFP_NOIO, &op->bio);
>   }
>   
>   static void end_discard(struct discard_op *op, int r)
> @@ -1113,9 +1113,7 @@ static void passdown_double_checking_shared_status(struct dm_thin_new_mapping *m
>   				break;
>   		}
>   
> -		r = issue_discard(&op, b, e);
> -		if (r)
> -			goto out;
> +		issue_discard(&op, b, e);
>   
>   		b = e;
>   	}
> @@ -1188,8 +1186,8 @@ static void process_prepared_discard_passdown_pt1(struct dm_thin_new_mapping *m)
>   		struct discard_op op;
>   
>   		begin_discard(&op, tc, discard_parent);
> -		r = issue_discard(&op, m->data_block, data_end);
> -		end_discard(&op, r);
> +		issue_discard(&op, m->data_block, data_end);
> +		end_discard(&op, 0);
>   	}
>   }
>   
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 7b5c5967568f..aeb62df39828 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -9132,8 +9132,8 @@ void md_submit_discard_bio(struct mddev *mddev, struct md_rdev *rdev,
>   {
>   	struct bio *discard_bio = NULL;
>   
> -	if (__blkdev_issue_discard(rdev->bdev, start, size, GFP_NOIO,
> -			&discard_bio) || !discard_bio)
> +	__blkdev_issue_discard(rdev->bdev, start, size, GFP_NOIO, &discard_bio);
> +	if (!discard_bio)
>   		return;
>   
>   	bio_chain(discard_bio, bio);

-- 
Thanks
Kuai