linux-kernel - Re: [dm-devel] [PATCH 23/41] dm: implement REQ

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Message-ID: <4C84CD18.6060906@redhat.com>
Date:	Mon, 06 Sep 2010 13:14:32 +0200
From:	Milan Broz <mbroz@...hat.com>
To:	device-mapper development <dm-devel@...hat.com>
CC:	Tejun Heo <tj@...nel.org>, jaxboe@...ionio.com,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-scsi@...r.kernel.org, linux-ide@...r.kernel.org,
	linux-raid@...r.kernel.org, hch@....de,
	konishi.ryusuke@....ntt.co.jp, James.Bottomley@...e.de,
	tytso@....edu, chris.mason@...cle.com, swhiteho@...hat.com,
	vst@...b.net, jack@...e.cz, rwheeler@...hat.com, hare@...e.de,
	neilb@...e.de, rusty@...tcorp.com.au, mst@...hat.com,
	snitzer@...hat.com, k-ueda@...jp.nec.com, mpatocka@...hat.com
Subject: Re: [dm-devel] [PATCH 23/41] dm: implement REQ_FLUSH/FUA support
 for	bio-based dm

On 09/03/2010 12:29 PM, Tejun Heo wrote:

> +++ b/drivers/md/dm-crypt.c
> @@ -1278,7 +1278,7 @@ static int crypt_map(struct dm_target *ti, struct bio *bio,
>  	struct dm_crypt_io *io;
>  	struct crypt_config *cc;
>  
> -	if (unlikely(bio_empty_barrier(bio))) {
> +	if (bio->bi_rw & REQ_FLUSH) {
>  		cc = ti->private;
>  		bio->bi_bdev = cc->dev->bdev;
>  		return DM_MAPIO_REMAPPED;

...

> +++ b/drivers/md/dm.c
> @@ -1400,14 +1391,22 @@ static void __split_and_process_bio(struct mapped_device *md, struct bio *bio)
>  	ci.io->md = md;
>  	spin_lock_init(&ci.io->endio_lock);
>  	ci.sector = bio->bi_sector;
> -	ci.sector_count = bio_sectors(bio);
> -	if (unlikely(bio_empty_barrier(bio)))
> +	if (!(bio->bi_rw & REQ_FLUSH))
> +		ci.sector_count = bio_sectors(bio);
> +	else {
> +		/* all FLUSH bio's reaching here should be empty */
> +		WARN_ON_ONCE(bio_has_data(bio));
>  		ci.sector_count = 1;
> +	}


I would add BUG_ON(bio_has_data(bio)) either to dm-crypt target or directly to DM core
in this path.

Note that empty barrier request bypass encryption layer now in dm-crypt, so if some bio
with data payload reach it after the change, it causes data corruption
(moreover plain data reach the disk directly).

Milan
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