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
> if (s->failed == 2) {
> dev = &sh->dev[s->failed_num[1]];
> s->locked++;
> --
> 2.20.1
>
