Re: md_raid: mdX_raid6 looping after sync_action "check" to "idle" transition

[Guoqing Jiang]

Hi Donald,

On 12/2/20 18:28, Donald Buczek wrote:
> 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;
>                      }

I think you can add the check of RECOVERY_CHECK in above part instead of 
add a new part.

>      +               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:

Without the patch, md0 was good while md1 was locked. So the patch 
switches the status of the two arrays, a little weird ...

What is the stack of the process? I guess it is same as the stack of 
23333 in your previous mail, but just to confirm.

>      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.

Could be, if so, then I think md_done_sync was not triggered by the path 
md0_raid6 -> ... -> handle_stripe.

I'd suggest to compare the stacks between md0 and md1 to find the 
difference.

Thanks,
Guoqing