Hi Nigel,
On Thu, Apr 11, 2019 at 10:21 AM Song Liu <liu.song.a23@xxxxxxxxx> wrote:
>
> On Tue, Apr 9, 2019 at 12:26 PM Nigel Croxon <ncroxon@xxxxxxxxxx> wrote:
> >
> >
> > On 4/9/19 2:09 PM, John Stoffel wrote:
> > >>>>>> "Dan" == Dan Williams <dan.j.williams@xxxxxxxxx> writes:
> > > Dan> On Mon, Apr 8, 2019 at 4:18 PM Song Liu <liu.song.a23@xxxxxxxxx> wrote:
> > > Dan> [..]
> > >>>>> To trigger this issue, you not only need a failed disk but to also
> > >>>>> perform a scrubbing operation. The customer's systems both crashed
> > >>>>> early Sunday morning when the raid-check script is run by default from cron.
> > >>>> Ok, I follow this, but I come to a different answer on the required
> > >>>> fix. I think it is simply the following to preserve the writeback
> > >>>> action after the parity check, because we need the failed Q slot to be
> > >>>> written back if we're recovering. P will be not up-to-date because it
> > >>>> was checked with the good disks, but sh->ops.zero_sum_result will be
> > >>>> 0, so that will skip the writeback of a !uptodate P value.
> > >>>>
> > >>>> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> > >>>> index c033bfcb209e..e2eb59289346 100644
> > >>>> --- a/drivers/md/raid5.c
> > >>>> +++ b/drivers/md/raid5.c
> > >>>> @@ -4187,7 +4187,6 @@ static void handle_parity_checks6(struct r5conf
> > >>>> *conf, struct stripe_head *sh,
> > >>>> /* now write out any block on a failed drive,
> > >>>> * or P or Q if they were recomputed
> > >>>> */
> > >>>> - BUG_ON(s->uptodate < disks - 1); /* We don't need Q to
> > >>>> recover */
> > >>> Thanks Dan!
> > >>>
> > >>> Would it make sense to rework the check as
> > >>>
> > >>> BUG_ON(s->uptodate < disks - 2);
> > > Dan> I think the problem is that any 'uptodate' vs 'disks' check is
> > > Dan> not precise enough in this path. What might be better is to put
> > > Dan> "WARN_ON(!test_bit(R5_UPTODATE, &dev->flags)" on the devices that
> > > Dan> might try to kick off writes and then skip the action. Better to
> > > Dan> prevent the raid driver from taking unexpected action *and* keep
> > > Dan> the system alive vs killing the machine with BUG_ON.
> > >
> > > Dan> BUG_ON has fallen out of favor for exception reporting since
> > > Dan> those assertions were introduced.
> > >
> > > And since it' causes the system to crash... it's super annoying when
> > > the rest of the system is working fine. Please only use a WARN_ON,
> > > and maybe even set the RAID volume readonly, etc. But don't bring
> > > down the rest of the system if possible.
> > >
> > > John
> >
> > I reverted the first patch as it made its way upstream.
> >
> > Testing this change now.
> >
> > ---
> >
> > drivers/md/raid5.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> > index c033bfcb209e..660ca3af2914 100644
> > --- a/drivers/md/raid5.c
> > +++ b/drivers/md/raid5.c
> > @@ -4187,7 +4187,7 @@ static void handle_parity_checks6(struct r5conf
> > *conf, struct stripe_head *sh,
> > /* now write out any block on a failed drive,
> > * or P or Q if they were recomputed
> > */
> > - BUG_ON(s->uptodate < disks - 1); /* We don't need Q to recover */
> > + WARN_ON(s->uptodate < disks - 2); /* We don't need Q to recover */
>
> I think this WARN_ON() is the best way to go, though the comment "don't need Q"
> needs some revise.
>
> Nigel, how does this work in your tests?
>
> Thanks,
> Song
Could you please share updates about the tests?
Thanks,
Song
>
> > if (s->failed == 2) {
> > dev = &sh->dev[s->failed_num[1]];
> > s->locked++;
> > --
> > 2.20.1
> >
