[dm-devel] dm-flakey NOT to return -EIO on READ?

[Lukas Herbolt]

Thanks Mike for fixing.
This was my first attempt to fix something in kernel so I wasn't sure about
the patch itself.
 - Lukas

On Fri, Jul 29, 2016 at 7:30 PM, Mike Snitzer <snitzer at redhat.com> wrote:

> On Fri, Jul 29 2016 at 10:35am -0400,
> Mike Snitzer <snitzer at redhat.com> wrote:
>
> > On Fri, Jul 29 2016 at 10:31am -0400,
> > Lukas Herbolt <lherbolt at redhat.com> wrote:
> >
> > >  - http://people.redhat.com/~lherbolt/dm-flakey/v4.7-dm_flakey.tar.gz
> > >
> > > Lukas
> >
> > Please post an incremental patch relative to 4.7 or latest Linus
> > kernel.  Don't make people suffer with tarballs of whatever you've
> > packaged above.
>
> I pulled out your incremental diff.  Your proposed fix isn't correct.  It
> breaks the corrupt_bio_byte feature.  We cannot blindly drop reads early
> in flakey_map(), like you've proposed, because the corrupt_bio_byte
> feature relies on corrupt data being returned on read during the
> down_interval.
>
> The issue reported is: reads aren't dropped during the "down_interval".
>
> I do agree that this needs fixing, and it was commit a3998799fb4df ("dm
> flakey: add corrupt_bio_byte feature") that caused this regression.
>
> But a fix must not break the corrupt_bio_byte feature.
>
> This fix should resolve the problem, I'll be staging it to go upstream
> during the 4.8-rc cycle (Akira, please test to verify your test fails as
> expected now):
>
> From: Mike Snitzer <snitzer at redhat.com>
> Date: Fri, 29 Jul 2016 13:19:55 -0400
> Subject: [PATCH] dm flakey: error READ bios during the down_interval
>
> When the corrupt_bio_byte feature was introduced it caused READ bios to
> no longer be errored with -EIO during the down_interval.  This had to do
> with the complexity of needing to submit READs if the corrupt_bio_byte
> feature was used.
>
> Fix it so READ bios are properly errored with -EIO; doing so early in
> flakey_map() as long as there isn't a match for the corrupt_bio_byte
> feature.
>
> Fixes: a3998799fb4df ("dm flakey: add corrupt_bio_byte feature")
> Reported-by: Akira Hayakawa <ruby.wktk at gmail.com>
> Signed-off-by: Mike Snitzer <snitzer at redhat.com>
> Cc: stable at vger.kernel.org
> ---
>  drivers/md/dm-flakey.c | 23 +++++++++++++++--------
>  1 file changed, 15 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/md/dm-flakey.c b/drivers/md/dm-flakey.c
> index 29b99fb..19db13e 100644
> --- a/drivers/md/dm-flakey.c
> +++ b/drivers/md/dm-flakey.c
> @@ -289,10 +289,16 @@ static int flakey_map(struct dm_target *ti, struct
> bio *bio)
>                 pb->bio_submitted = true;
>
>                 /*
> -                * Map reads as normal.
> +                * Map reads as normal only if corrupt_bio_byte set.
>                  */
> -               if (bio_data_dir(bio) == READ)
> -                       goto map_bio;
> +               if (bio_data_dir(bio) == READ) {
> +                       /* If flags were specified, only corrupt those
> that match. */
> +                       if (fc->corrupt_bio_byte && (fc->corrupt_bio_rw ==
> READ) &&
> +                           all_corrupt_bio_flags_match(bio, fc))
> +                               goto map_bio;
> +                       else
> +                               return -EIO;
> +               }
>
>                 /*
>                  * Drop writes?
> @@ -330,12 +336,13 @@ static int flakey_end_io(struct dm_target *ti,
> struct bio *bio, int error)
>
>         /*
>          * Corrupt successful READs while in down state.
> -        * If flags were specified, only corrupt those that match.
>          */
> -       if (fc->corrupt_bio_byte && !error && pb->bio_submitted &&
> -           (bio_data_dir(bio) == READ) && (fc->corrupt_bio_rw == READ) &&
> -           all_corrupt_bio_flags_match(bio, fc))
> -               corrupt_bio_data(bio, fc);
> +       if (!error && pb->bio_submitted && (bio_data_dir(bio) == READ)) {
> +               if (fc->corrupt_bio_byte)
> +                       corrupt_bio_data(bio, fc);
> +               else
> +                       return -EIO;
> +       }
>
>         return error;
>  }
> --
> 2.7.4 (Apple Git-66)
>
>


-- 
Lukas Herbolt
RHCE, RH436, BSc, SSc
Senior Technical Support Engineer
Global Support Services (GSS)
Email:    lherbolt at redhat.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://listman.redhat.com/archives/dm-devel/attachments/20160729/5c7944b7/attachment.htm>