Re: [PATCH] md/raid1: add error handling of read error from FailFast device

From: Gi-Oh Kim
Date: Wed May 02 2018 - 08:12:37 EST

On Wed, May 2, 2018 at 1:08 PM, Gioh Kim <gi-oh.kim@xxxxxxxxxxxxxxxx> wrote:
> Current handle_read_error() function calls fix_read_error()
> only if md device is RW and rdev does not include FailFast flag.
> It does not handle a read error from a RW device including
> FailFast flag.
>
> I am not sure it is intended. But I found that write IO error
> sets rdev faulty. The md module should handle the read IO error and
> write IO error equally. So I think read IO error should set rdev faulty.
>
> Signed-off-by: Gioh Kim <gi-oh.kim@xxxxxxxxxxxxxxxx>
> ---
> drivers/md/raid1.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> index e9e3308cb0a7..4445179aa4c8 100644
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
> @@ -2474,6 +2474,8 @@ static void handle_read_error(struct r1conf *conf, struct r1bio *r1_bio)
> fix_read_error(conf, r1_bio->read_disk,
> r1_bio->sector, r1_bio->sectors);
> unfreeze_array(conf);
> + } else if (mddev->ro == 0 && test_bit(FailFast, &rdev->flags)) {
> + md_error(mddev, rdev);
> } else {
> r1_bio->bios[r1_bio->read_disk] = IO_BLOCKED;
> }
> --
> 2.14.1
>

I think it would be helpful to show how I tested it.

As following I used Ubuntu 17.10 and mdadm v4.0.
# cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=17.10
DISTRIB_CODENAME=artful
DISTRIB_DESCRIPTION="Ubuntu 17.10"
# uname -a
Linux ws00837 4.13.0-16-generic #19-Ubuntu SMP Wed Oct 11 18:35:14 UTC
2017 x86_64 x86_64 x86_64 GNU/Linux
# mdadm --version
mdadm - v4.0 - 2017-01-09

Following is how I generated the read IO error and checked md device.
After read IO, no device was set as faulty

# modprobe scsi_debug num_parts=2
# man mdadm
# mdadm -C /dev/md111 --failfast -l 1 -n 2 /dev/sdc1 /dev/sdc2
mdadm: Note: this array has metadata at the start and
may not be suitable as a boot device. If you plan to
store '/boot' on this device please ensure that
your boot-loader understands md/v1.x metadata, or use
--metadata=0.90
mdadm: largest drive (/dev/sdc2) exceeds size (3904K) by more than 1%
Continue creating array? y
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md111 started.
# mdadm -D /dev/md111
/dev/md111:
Version : 1.2
Creation Time : Wed May 2 10:55:35 2018
Raid Level : raid1
Array Size : 3904
Used Dev Size : 3904
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent

Update Time : Wed May 2 10:55:36 2018
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0

Name : ws00837:111 (local to host ws00837)
UUID : 9f214193:03cf7c97:3208da22:d6ab8a13
Events : 17

Number Major Minor RaidDevice State
0 8 33 0 active sync failfast /dev/sdc1
1 8 34 1 active sync failfast /dev/sdc2
# cat /proc/mdstat
Personalities : [raid1]
md111 : active raid1 sdc2[1] sdc1[0]
3904 blocks super 1.2 [2/2] [UU]

unused devices: <none>
# echo -1 > /sys/module/scsi_debug/parameters/every_nth && echo 4 >
/sys/module/scsi_debug/parameters/opts
# dd if=/dev/md111 of=/dev/null bs=4K count=1 iflag=direct &
[1] 6322
# dd: error reading '/dev/md111': Input/output error
0+0 records in
0+0 records out
0 bytes copied, 124,376 s, 0,0 kB/s

[1]+ Exit 1 dd if=/dev/md111 of=/dev/null bs=4K
count=1 iflag=direct
# mdadm -D /dev/md111/dev/md111:
Version : 1.2
Creation Time : Wed May 2 10:55:35 2018
Raid Level : raid1
Array Size : 3904
Used Dev Size : 3904
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent

Update Time : Wed May 2 10:55:36 2018
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0

Number Major Minor RaidDevice State
0 8 33 0 active sync failfast /dev/sdc1
1 8 34 1 active sync failfast /dev/sdc2


Following is how I generated the write IO error and checked md device.
After write IO error, one device was set as faulty.

gohkim@ws00837:~$ sudo modprobe scsi_debug num_parts=2
gohkim@ws00837:~$ sudo mdadm -C /dev/md111 --failfast -l 1 -n 2
/dev/sdc1 /dev/sdc2
mdadm: Note: this array has metadata at the start and
may not be suitable as a boot device. If you plan to
store '/boot' on this device please ensure that
your boot-loader understands md/v1.x metadata, or use
--metadata=0.90
mdadm: largest drive (/dev/sdc2) exceeds size (3904K) by more than 1%
Continue creating array? y
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md111 started.
gohkim@ws00837:~$ sudo mdadm -D /dev/md111
/dev/md111:
Version : 1.2
Creation Time : Wed May 2 14:03:30 2018
Raid Level : raid1
Array Size : 3904
Used Dev Size : 3904
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent

Update Time : Wed May 2 14:03:31 2018
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0

Name : ws00837:111 (local to host ws00837)
UUID : ba51fe65:c517a25a:a381ccc5:3617322b
Events : 17

Number Major Minor RaidDevice State
0 8 33 0 active sync failfast /dev/sdc1
1 8 34 1 active sync failfast /dev/sdc2
gohkim@ws00837:~$ echo -1 | sudo tee /sys/module/scsi_debug/parameters/every_nth
-1
gohkim@ws00837:~$ echo 4 | sudo tee /sys/module/scsi_debug/parameters/opts
4
gohkim@ws00837:~$ sudo dd if=/dev/zero of=/dev/md111 bs=4K count=1
oflag=direct &
[1] 13081
gohkim@ws00837:~$ dd: error writing '/dev/md111': Input/output error
1+0 records in
0+0 records out
0 bytes copied, 184,523 s, 0,0 kB/s

[1]+ Exit 1 sudo dd if=/dev/zero of=/dev/md111 bs=4K
count=1 oflag=direct
gohkim@ws00837:~$ sudo mdadm -D /dev/md111
/dev/md111:
Version : 1.2
Creation Time : Wed May 2 14:03:30 2018
Raid Level : raid1
Array Size : 3904
Used Dev Size : 3904
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent

Update Time : Wed May 2 14:07:47 2018
State : clean, degraded
Active Devices : 1
Working Devices : 1
Failed Devices : 1
Spare Devices : 0

Number Major Minor RaidDevice State
0 8 33 0 active sync failfast /dev/sdc1
- 0 0 1 removed

1 8 34 - faulty failfast /dev/sdc2



--
GIOH KIM
Linux Kernel Entwickler

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