Re: [PATCH 1/3] raid0, linear, md: add error_handlers for raid0 and linear

[Xiao Ni <xni@redhat.com>]

On Fri, Dec 17, 2021 at 10:00 AM Guoqing Jiang <guoqing.jiang@linux.dev> wrote:
>
>
>
> On 12/16/21 10:52 PM, Mariusz Tkaczyk wrote:
> > Patch 62f7b1989c0 ("md raid0/linear: Mark array as 'broken' and fail BIOs
> > if a member is gone") allowed to finish writes earlier (before level
> > dependent actions) for non-redundant arrays.
> >
> > To achieve that MD_BROKEN is added to mddev->flags if drive disappearance
> > is detected. This is done in is_mddev_broken() which is confusing and not
> > consistent with other levels where error_handler() is used.
> > This patch adds appropriate error_handler for raid0 and linear.
> >
> > It also adopts md_error(), we only want to call .error_handler for those
> > levels. mddev->pers->sync_request is additionally checked, its existence
> > implies a level with redundancy.
> >
> > Usage of error_handler causes that disk failure can be requested from
> > userspace. User can fail the array via #mdadm --set-faulty command. This
> > is not safe and will be fixed in mdadm. It is correctable because failed
> > state is not recorded in the metadata. After next assembly array will be
> > read-write again. For safety reason is better to keep MD_BROKEN in
> > runtime only.
> >
> > Signed-off-by: Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>
> > ---
> >   drivers/md/md-linear.c | 15 ++++++++++++++-
> >   drivers/md/md.c        |  6 +++++-
> >   drivers/md/md.h        | 10 ++--------
> >   drivers/md/raid0.c     | 15 ++++++++++++++-
> >   4 files changed, 35 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/md/md-linear.c b/drivers/md/md-linear.c
> > index 1ff51647a682..415d2615d17a 100644
> > --- a/drivers/md/md-linear.c
> > +++ b/drivers/md/md-linear.c
> > @@ -233,7 +233,8 @@ static bool linear_make_request(struct mddev *mddev, struct bio *bio)
> >                    bio_sector < start_sector))
> >               goto out_of_bounds;
> >
> > -     if (unlikely(is_mddev_broken(tmp_dev->rdev, "linear"))) {
> > +     if (unlikely(is_rdev_broken(tmp_dev->rdev))) {
> > +             md_error(mddev, tmp_dev->rdev);
> >               bio_io_error(bio);
> >               return true;
> >       }
> > @@ -281,6 +282,17 @@ static void linear_status (struct seq_file *seq, struct mddev *mddev)
> >       seq_printf(seq, " %dk rounding", mddev->chunk_sectors / 2);
> >   }
> >
> > +static void linear_error(struct mddev *mddev, struct md_rdev *rdev)
> > +{
> > +     char b[BDEVNAME_SIZE];
> > +
> > +     if (!test_and_set_bit(MD_BROKEN, &rdev->mddev->flags))
> > +             pr_crit("md/linear%s: Disk failure on %s detected.\n"
> > +                     "md/linear:%s: Cannot continue, failing array.\n",
> > +                     mdname(mddev), bdevname(rdev->bdev, b),
> > +                     mdname(mddev));
> > +}
> > +
>
> Do you consider to use %pg to print block device?
>
> >   static void linear_quiesce(struct mddev *mddev, int state)
> >   {
> >   }
> > @@ -297,6 +309,7 @@ static struct md_personality linear_personality =
> >       .hot_add_disk   = linear_add,
> >       .size           = linear_size,
> >       .quiesce        = linear_quiesce,
> > +     .error_handler  = linear_error,
> >   };
> >
> >   static int __init linear_init (void)
> > diff --git a/drivers/md/md.c b/drivers/md/md.c
> > index e8666bdc0d28..f888ef197765 100644
> > --- a/drivers/md/md.c
> > +++ b/drivers/md/md.c
> > @@ -7982,7 +7982,11 @@ void md_error(struct mddev *mddev, struct md_rdev *rdev)
> >
> >       if (!mddev->pers || !mddev->pers->error_handler)
> >               return;
> > -     mddev->pers->error_handler(mddev,rdev);
> > +     mddev->pers->error_handler(mddev, rdev);
> > +
> > +     if (!mddev->pers->sync_request)
> > +             return;
> > +
>
> What is the reason of the above change? I suppose dm event can be missed.

Hi Guoqing

What's the dm event here? From my understanding, this patch only wants
to set MD_BROKEN
in error handler. Now raid0 and linear only need to do this job in
md_error. It checks ->sync_request
here and can return for raid0 and linear. In the error handler raid0
and linear already set MD_BROKEN.

Best Regards
Xiao