>>>>> "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
