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