From: BingJing Chang bingjingc@synology.com
[ Upstream commit d63e2fc804c46e50eee825c5d3a7228e07048b47 ]
During raid5 replacement, the stripes can be marked with R5_NeedReplace flag. Data can be read from being-replaced devices and written to replacing spares without reading all other devices. (It's 'replace' mode. s.replacing = 1) If a being-replaced device is dropped, the replacement progress will be interrupted and resumed with pure recovery mode. However, existing stripes before being interrupted cannot read from the dropped device anymore. It prints lots of WARN_ON messages. And it results in data corruption because existing stripes write problematic data into its replacement device and update the progress.
# Erase disks (1MB + 2GB) dd if=/dev/zero of=/dev/sda bs=1MB count=2049 dd if=/dev/zero of=/dev/sdb bs=1MB count=2049 dd if=/dev/zero of=/dev/sdc bs=1MB count=2049 dd if=/dev/zero of=/dev/sdd bs=1MB count=2049 mdadm -C /dev/md0 -amd -R -l5 -n3 -x0 /dev/sd[abc] -z 2097152 # Ensure array stores non-zero data dd if=/root/data_4GB.iso of=/dev/md0 bs=1MB # Start replacement mdadm /dev/md0 -a /dev/sdd mdadm /dev/md0 --replace /dev/sda
Then, Hot-plug out /dev/sda during recovery, and wait for recovery done. echo check > /sys/block/md0/md/sync_action cat /sys/block/md0/md/mismatch_cnt # it will be greater than 0.
Soon after you hot-plug out /dev/sda, you will see many WARN_ON messages. The replacement recovery will be interrupted shortly. After the recovery finishes, it will result in data corruption.
Actually, it's just an unhandled case of replacement. In commit <f94c0b6658c7> (md/raid5: fix interaction of 'replace' and 'recovery'.), if a NeedReplace device is not UPTODATE then that is an error, the commit just simply print WARN_ON but also mark these corrupted stripes with R5_WantReplace. (it means it's ready for writes.)
To fix this case, we can leverage 'sync and replace' mode mentioned in commit <9a3e1101b827> (md/raid5: detect and handle replacements during recovery.). We can add logics to detect and use 'sync and replace' mode for these stripes.
Reported-by: Alex Chen alexchen@synology.com Reviewed-by: Alex Wu alexwu@synology.com Reviewed-by: Chung-Chiang Cheng cccheng@synology.com Signed-off-by: BingJing Chang bingjingc@synology.com Signed-off-by: Shaohua Li shli@fb.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- drivers/md/raid5.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c index d59b861764a1..0841d8f10a58 100644 --- a/drivers/md/raid5.c +++ b/drivers/md/raid5.c @@ -4190,6 +4190,12 @@ static void analyse_stripe(struct stripe_head *sh, struct stripe_head_state *s) s->failed++; if (rdev && !test_bit(Faulty, &rdev->flags)) do_recovery = 1; + else if (!rdev) { + rdev = rcu_dereference( + conf->disks[i].replacement); + if (rdev && !test_bit(Faulty, &rdev->flags)) + do_recovery = 1; + } } } if (test_bit(STRIPE_SYNCING, &sh->state)) {