On Mon, Sep 06 2010 at 7:14am -0400,
Milan Broz <mbroz@xxxxxxxxxx> wrote:
> 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.
I agree, that WARN_ON_ONCE should be changed to BUG_ON. This is a
guarantee that the block layer now provides so it seems correct to have
the DM core bug if that guarantee isn't actually provided.
> 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).
Given the consequences, it wouldn't hurt to BUG_ON() in dm-crypt too.
It's redundant if the DM core will also BUG_ON() but it serves as a
dm-crypt safety-net/documentation.
Mike
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