linux-kernel - Re: [PATCH v2 12/26] raid1: use bio

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Date:	Tue, 11 Sep 2012 14:59:13 +1000
From:	NeilBrown <neilb@...e.de>
To:	Kent Overstreet <koverstreet@...gle.com>
Cc:	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, axboe@...nel.dk, tj@...nel.org
Subject: Re: [PATCH v2 12/26] raid1: use bio_reset()

On Mon, 10 Sep 2012 17:22:23 -0700 Kent Overstreet <koverstreet@...gle.com>
wrote:

> I couldn't figure out what sbio->bi_end_io in process_checks() was
> supposed to be, so I took the easy way out.

Almost.
You save 'sbio->bi_end_io' to 'bi_end_io', then do nothing with it...

A little way above the 'fixup the bio for reuse' comment you'll find:

		struct bio *sbio = r1_bio->bios[i];
....
		if (r1_bio->bios[i]->bi_end_io != end_sync_read)
			continue;

which implies that if we don't 'continue', then sbio->bi_end_io ==
end_sync_read.

So I suspect you want to add
    sbio->bi_end_io = end_sync_read;
somewhere after the 'bio_reset()'.

If you happened to also fix that 'if' that I quoted so that it reads:

     if (sbio->bi_end_io != end_sync_read)
           continue;

I wouldn't complain at all :-)

Thanks,
NeilBrown


> 
> Signed-off-by: Kent Overstreet <koverstreet@...gle.com>
> CC: Jens Axboe <axboe@...nel.dk>
> CC: NeilBrown <neilb@...e.de>
> ---
>  drivers/md/raid1.c | 22 +++++-----------------
>  1 file changed, 5 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> index ee85154..bd3e3b9 100644
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
> @@ -1835,6 +1835,7 @@ static int process_checks(struct r1bio *r1_bio)
>  	int primary;
>  	int i;
>  	int vcnt;
> +	bio_end_io_t *bi_end_io;
>  
>  	for (primary = 0; primary < conf->raid_disks * 2; primary++)
>  		if (r1_bio->bios[primary]->bi_end_io == end_sync_read &&
> @@ -1876,13 +1877,11 @@ static int process_checks(struct r1bio *r1_bio)
>  			continue;
>  		}
>  		/* fixup the bio for reuse */
> +		bi_end_io = sbio->bi_end_io;
> +		bio_reset(sbio);
> +
>  		sbio->bi_vcnt = vcnt;
>  		sbio->bi_size = r1_bio->sectors << 9;
> -		sbio->bi_idx = 0;
> -		sbio->bi_phys_segments = 0;
> -		sbio->bi_flags &= ~(BIO_POOL_MASK - 1);
> -		sbio->bi_flags |= 1 << BIO_UPTODATE;
> -		sbio->bi_next = NULL;
>  		sbio->bi_sector = r1_bio->sector +
>  			conf->mirrors[i].rdev->data_offset;
>  		sbio->bi_bdev = conf->mirrors[i].rdev->bdev;
> @@ -2426,18 +2425,7 @@ static sector_t sync_request(struct mddev *mddev, sector_t sector_nr, int *skipp
>  	for (i = 0; i < conf->raid_disks * 2; i++) {
>  		struct md_rdev *rdev;
>  		bio = r1_bio->bios[i];
> -
> -		/* take from bio_init */
> -		bio->bi_next = NULL;
> -		bio->bi_flags &= ~(BIO_POOL_MASK-1);
> -		bio->bi_flags |= 1 << BIO_UPTODATE;
> -		bio->bi_rw = READ;
> -		bio->bi_vcnt = 0;
> -		bio->bi_idx = 0;
> -		bio->bi_phys_segments = 0;
> -		bio->bi_size = 0;
> -		bio->bi_end_io = NULL;
> -		bio->bi_private = NULL;
> +		bio_reset(bio);
>  
>  		rdev = rcu_dereference(conf->mirrors[i].rdev);
>  		if (rdev == NULL ||


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