While adding an additional drive to a raid6 array, the reshape stalled
at about 13% complete and any I/O operations on the array hung,
creating an effective soft lock. The kernel reported a hung task in
mdXX_reshape thread and I had to use magic sysrq to recover as systemd
hung as well.
I first suspected an issue with one of the underlying block devices and
as precaution I recovered the data in read only mode to a new array, but
it turned out to be in the RAID layer as I was able to recreate the
issue from a superblock dump in sparse files.
After poking around some I discovered that I had somehow propagated the
bad block list to several devices in the array such that a few blocks
were unreable. The bad read reported correctly in userspace during
recovery, but it wasn't obvious that it was from a bad block list
metadata at the time and instead confirmed my bias suspecting hardware
issues
I was able to reproduce the issue with a minimal test case using small
loopback devices. I put a script for this in a github repository:
https://github.com/dougvj/md_badblock_reshape_stall_test
This patch handles bad reads during a reshape by unmarking the
STRIPE_EXPANDING and STRIPE_EXPAND_READY bits effectively skipping the
stripe and then reports the issue in dmesg.
Signed-off-by: Doug V Johnson <dougvj@xxxxxxxxxx>
---
drivers/md/raid5.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 5c79429acc64..0ae9ac695d8e 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -4987,6 +4987,14 @@ static void handle_stripe(struct stripe_head *sh)
handle_failed_stripe(conf, sh, &s, disks);
if (s.syncing + s.replacing)
handle_failed_sync(conf, sh, &s);
+ if (test_bit(STRIPE_EXPANDING, &sh->state)) {
+ pr_warn_ratelimited("md/raid:%s: read error during reshape at %lu",
+ mdname(conf->mddev),
+ (unsigned long)sh->sector);
+ /* Abort the current stripe */
+ clear_bit(STRIPE_EXPANDING, &sh->state);
+ clear_bit(STRIPE_EXPAND_READY, &sh->state);
+ }
}
/* Now we check to see if any write operations have recently