Re: md_raid: mdX_raid6 looping after sync_action "check" to "idle" transition
From: Donald Buczek
Date: Wed Dec 02 2020 - 12:29:14 EST
Dear Guoqing,
unfortunately the patch didn't fix the problem (unless I messed it up with my logging). This is what I used:
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -9305,6 +9305,14 @@ void md_check_recovery(struct mddev *mddev)
clear_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
goto unlock;
}
+ if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) &&
+ (!test_bit(MD_RECOVERY_DONE, &mddev->recovery) ||
+ test_bit(MD_RECOVERY_CHECK, &mddev->recovery))) {
+ /* resync/recovery still happening */
+ pr_info("md: XXX BUGFIX applied\n");
+ clear_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
+ goto unlock;
+ }
if (mddev->sync_thread) {
md_reap_sync_thread(mddev);
goto unlock;
With pausing and continuing the check four times an hour, I could trigger the problem after about 48 hours. This time, the other device (md0) has locked up on `echo idle > /sys/devices/virtual/block/md0/md/sync_action` , while the check of md1 is still ongoing:
Personalities : [linear] [raid0] [raid1] [raid6] [raid5] [raid4] [multipath]
md1 : active raid6 sdk[0] sdj[15] sdi[14] sdh[13] sdg[12] sdf[11] sde[10] sdd[9] sdc[8] sdr[7] sdq[6] sdp[5] sdo[4] sdn[3] sdm[2] sdl[1]
109394518016 blocks super 1.2 level 6, 512k chunk, algorithm 2 [16/16] [UUUUUUUUUUUUUUUU]
[=>...................] check = 8.5% (666852112/7813894144) finish=1271.2min speed=93701K/sec
bitmap: 0/59 pages [0KB], 65536KB chunk
md0 : active raid6 sds[0] sdah[15] sdag[16] sdaf[13] sdae[12] sdad[11] sdac[10] sdab[9] sdaa[8] sdz[7] sdy[6] sdx[17] sdw[4] sdv[3] sdu[2] sdt[1]
109394518016 blocks super 1.2 level 6, 512k chunk, algorithm 2 [16/16] [UUUUUUUUUUUUUUUU]
[>....................] check = 0.2% (19510348/7813894144) finish=253779.6min speed=511K/sec
bitmap: 0/59 pages [0KB], 65536KB chunk
after 1 minute:
Personalities : [linear] [raid0] [raid1] [raid6] [raid5] [raid4] [multipath]
md1 : active raid6 sdk[0] sdj[15] sdi[14] sdh[13] sdg[12] sdf[11] sde[10] sdd[9] sdc[8] sdr[7] sdq[6] sdp[5] sdo[4] sdn[3] sdm[2] sdl[1]
109394518016 blocks super 1.2 level 6, 512k chunk, algorithm 2 [16/16] [UUUUUUUUUUUUUUUU]
[=>...................] check = 8.6% (674914560/7813894144) finish=941.1min speed=126418K/sec
bitmap: 0/59 pages [0KB], 65536KB chunk
md0 : active raid6 sds[0] sdah[15] sdag[16] sdaf[13] sdae[12] sdad[11] sdac[10] sdab[9] sdaa[8] sdz[7] sdy[6] sdx[17] sdw[4] sdv[3] sdu[2] sdt[1]
109394518016 blocks super 1.2 level 6, 512k chunk, algorithm 2 [16/16] [UUUUUUUUUUUUUUUU]
[>....................] check = 0.2% (19510348/7813894144) finish=256805.0min speed=505K/sec
bitmap: 0/59 pages [0KB], 65536KB chunk
A data point, I didn't mention in my previous mail, is that the mdX_resync thread is not gone when the problem occurs:
buczek@done:/scratch/local/linux (v5.10-rc6-mpi)$ ps -Af|fgrep [md
root 134 2 0 Nov30 ? 00:00:00 [md]
root 1321 2 27 Nov30 ? 12:57:14 [md0_raid6]
root 1454 2 26 Nov30 ? 12:37:23 [md1_raid6]
root 5845 2 0 16:20 ? 00:00:30 [md0_resync]
root 5855 2 13 16:20 ? 00:14:11 [md1_resync]
buczek 9880 9072 0 18:05 pts/0 00:00:00 grep -F [md
buczek@done:/scratch/local/linux (v5.10-rc6-mpi)$ sudo cat /proc/5845/stack
[<0>] md_bitmap_cond_end_sync+0x12d/0x170
[<0>] raid5_sync_request+0x24b/0x390
[<0>] md_do_sync+0xb41/0x1030
[<0>] md_thread+0x122/0x160
[<0>] kthread+0x118/0x130
[<0>] ret_from_fork+0x1f/0x30
I guess, md_bitmap_cond_end_sync+0x12d is the `wait_event(bitmap->mddev->recovery_wait,atomic_read(&bitmap->mddev->recovery_active) == 0);` in md-bitmap.c.
Donald
On 01.12.20 10:29, Donald Buczek wrote:
Am 30.11.20 um 03:06 schrieb Guoqing Jiang:
On 11/28/20 13:25, Donald Buczek wrote:
Dear Linux mdraid people,
we are using raid6 on several servers. Occasionally we had failures, where a mdX_raid6 process seems to go into a busy loop and all I/O to the md device blocks. We've seen this on various kernel versions.
The last time this happened (in this case with Linux 5.10.0-rc4), I took some data.
The triggering event seems to be the md_check cron job trying to pause the ongoing check operation in the morning with
echo idle > /sys/devices/virtual/block/md1/md/sync_action
This doesn't complete. Here's /proc/stack of this process:
root@done:~/linux_problems/mdX_raid6_looping/2020-11-27# ps -fp 23333
UID PID PPID C STIME TTY TIME CMD
root 23333 23331 0 02:00 ? 00:00:00 /bin/bash /usr/bin/mdcheck --continue --duration 06:00
root@done:~/linux_problems/mdX_raid6_looping/2020-11-27# cat /proc/23333/stack
[<0>] kthread_stop+0x6e/0x150
[<0>] md_unregister_thread+0x3e/0x70
[<0>] md_reap_sync_thread+0x1f/0x1e0
[<0>] action_store+0x141/0x2b0
[<0>] md_attr_store+0x71/0xb0
[<0>] kernfs_fop_write+0x113/0x1a0
[<0>] vfs_write+0xbc/0x250
[<0>] ksys_write+0xa1/0xe0
[<0>] do_syscall_64+0x33/0x40
[<0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
Note, that md0 has been paused successfully just before.
What is the personality of md0? Is it also raid6?
Yes.
2020-11-27T02:00:01+01:00 done CROND[23333]: (root) CMD (/usr/bin/mdcheck --continue --duration "06:00")
2020-11-27T02:00:01+01:00 done root: mdcheck continue checking /dev/md0 from 10623180920
2020-11-27T02:00:01.382994+01:00 done kernel: [378596.606381] md: data-check of RAID array md0
2020-11-27T02:00:01+01:00 done root: mdcheck continue checking /dev/md1 from 11582849320
2020-11-27T02:00:01.437999+01:00 done kernel: [378596.661559] md: data-check of RAID array md1
2020-11-27T06:00:01.842003+01:00 done kernel: [392996.625147] md: md0: data-check interrupted.
2020-11-27T06:00:02+01:00 done root: pause checking /dev/md0 at 13351127680
2020-11-27T06:00:02.338989+01:00 done kernel: [392997.122520] md: md1: data-check interrupted.
[ nothing related following.... ]
After that, we see md1_raid6 in a busy loop:
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
2376 root 20 0 0 0 0 R 100.0 0.0 1387:38 md1_raid6
Seems the reap sync thread was trying to stop md1_raid6 while md1_raid6 was triggered again and again.
Also, all processes doing I/O do the md device block.
This is /proc/mdstat:
Personalities : [linear] [raid0] [raid1] [raid6] [raid5] [raid4] [multipath]
md1 : active raid6 sdk[0] sdj[15] sdi[14] sdh[13] sdg[12] sdf[11] sde[10] sdd[9] sdc[8] sdr[7] sdq[6] sdp[5] sdo[4] sdn[3] sdm[2] sdl[1]
109394518016 blocks super 1.2 level 6, 512k chunk, algorithm 2 [16/16] [UUUUUUUUUUUUUUUU]
[==================>..] check = 94.0% (7350290348/7813894144) finish=57189.3min speed=135K/sec
bitmap: 0/59 pages [0KB], 65536KB chunk
md0 : active raid6 sds[0] sdah[15] sdag[16] sdaf[13] sdae[12] sdad[11] sdac[10] sdab[9] sdaa[8] sdz[7] sdy[6] sdx[17] sdw[4] sdv[3] sdu[2] sdt[1]
109394518016 blocks super 1.2 level 6, 512k chunk, algorithm 2 [16/16] [UUUUUUUUUUUUUUUU]
bitmap: 0/59 pages [0KB], 65536KB chunk
So the RECOVERY_CHECK flag should be set, not sure if the simple changes
helps, but you may give it a try.
Thanks. I've copied the original condition block to execute before the modified one and added some logging to it to see, if the change actually triggers. I will pause and unpause the check frequently on a busy machine to get this code executed more often.
Best
Donald
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 98bac4f..e2697d0 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -9300,7 +9300,8 @@ void md_check_recovery(struct mddev *mddev)
md_update_sb(mddev, 0);
if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) &&
- !test_bit(MD_RECOVERY_DONE, &mddev->recovery)) {
+ (!test_bit(MD_RECOVERY_DONE, &mddev->recovery) ||
+ test_bit(MD_RECOVERY_CHECK, &mddev->recovery))) {
/* resync/recovery still happening */
clear_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
goto unlock;
Thanks,
Guoqing
--
Donald Buczek
buczek@xxxxxxxxxxxxx
Tel: +49 30 8413 1433