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Bug 1443144 - Grub2 does not detect MD raid (level 1) 1.0 superblocks on 4k block devices
Summary: Grub2 does not detect MD raid (level 1) 1.0 superblocks on 4k block devices
Keywords:
Status: CLOSED INSUFFICIENT_DATA
Alias: None
Product: Red Hat Enterprise Linux 7
Classification: Red Hat
Component: grub2
Version: 7.3
Hardware: All
OS: Linux
high
high
Target Milestone: rc
: 7.7
Assignee: Peter Jones
QA Contact: Release Test Team
URL:
Whiteboard:
Depends On: 1184945
Blocks: 1420851 1477664 1546815 1598750 1689420
TreeView+ depends on / blocked
 
Reported: 2017-04-18 15:08 UTC by Kyle Walker
Modified: 2023-07-05 12:30 UTC (History)
15 users (show)

Fixed In Version:
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
Environment:
Last Closed: 2019-06-13 09:12:28 UTC
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
IBM Linux Technology Center 153545 0 None None None 2019-07-08 05:08:31 UTC

Description Kyle Walker 2017-04-18 15:08:07 UTC 
Description of problem:
 Per the description above, Grub2 does not currently detect MD raid 1.0 superblocks when written to 4k block devices. The issue is only visible on disks that have 4K native sector sizes. 

See below example:

    Disk /dev/vdb: 10.7 GB, 10737418240 bytes, 2621440 sectors
    Units = sectors of 1 * 4096 = 4096 bytes
    Sector size (logical/physical): 4096 bytes / 4096 bytes
    I/O size (minimum/optimal): 4096 bytes / 4096 bytes
    Disk label type: dos
    Disk identifier: 0x6c5f13de

       Device Boot      Start         End      Blocks   Id  System
    /dev/vdb1             256      128255      512000   83  Linux
    /dev/vdb2          128256     2621439     9972736   83  Linux

    Disk /dev/vdc: 10.7 GB, 10737418240 bytes, 2621440 sectors
    Units = sectors of 1 * 4096 = 4096 bytes
    Sector size (logical/physical): 4096 bytes / 4096 bytes
    I/O size (minimum/optimal): 4096 bytes / 4096 bytes
    Disk label type: dos
    Disk identifier: 0x00000000

       Device Boot      Start         End      Blocks   Id  System
    /dev/vdc1             256      128255      512000   83  Linux
    /dev/vdc2          128256     2621439     9972736   83  Linux


Two (degraded) raid devices are created, using 1.0 and 1.2 metadata revisions.

    # cat /proc/mdstat 
    Personalities : [raid1] 
    md1 : active raid1 vdc1[1]
          511680 blocks super 1.2 [2/1] [_U]

    md0 : active raid1 vdb1[1]
          511936 blocks super 1.0 [2/1] [_U]

    unused devices: <none>

For the 1.2 superblock format, the following is visible:

    # grub2-probe --device /dev/md1 --target fs_uuid
    f2ebfe82-55ab-45a8-b391-39c77f3c489e

Whereas the 1.0 format, with the superblock at the end of the device, returns:

  # grub2-probe --device /dev/md0 --target fsuuid
  grub2-probe error disk mduuid/4589a761dde10c78a204bcfd705df061 not found.


Version-Release number of selected component (if applicable):
  grub2-2.02-0.44.el7.x86_64

How reproducible:
  Easily - With a 4k native storage device for boot

Steps to Reproduce:
1. Install a system

2. Migrate to a MD raid (level 1) metadata 1.0 configuration using the process outlined in the article below:

    How do I create /boot on mdadm RAID 1 after installation in RHEL 7? - Red Hat Customer Portal
    https://access.redhat.com/solutions/1360363

3. Issue a "grub2-probe --device /dev/md<device> --target fs_uuid" against the device which /boot is installed to

Actual results:

    # grub2-probe --device /dev/md0 --target fsuuid
    grub2-probe error disk mduuid/4589a761dde10c78a204bcfd705df061 not found.


Expected results:

    # grub2-probe --device /dev/md1 --target fs_uuid
    f2ebfe82-55ab-45a8-b391-39c77f3c489e


Additional info:
 Note, the issue was originally noted at installation-time as the default superblock format for PPC64 (PReP boot) systems is 1.0 according to the python-blivet library, used by the anaconda installer, code snippet below:

    def preCommitFixup(self, *args, **kwargs):
        """ Determine create parameters for this set """
        mountpoints = kwargs.pop("mountpoints")
        log_method_call(self, self.name, mountpoints)

        if "/boot" in mountpoints:
            bootmountpoint = "/boot"
        else:
            bootmountpoint = "/"

        # If we are used to boot from we cannot use 1.1 metadata
        if getattr(self.format, "mountpoint", None) == bootmountpoint or \
           getattr(self.format, "mountpoint", None) == "/boot/efi" or \
           self.format.type == "prepboot":
            self.metadataVersion = "1.0"

In short, if we install to a PPC64 system on 4k block disks and MD raid, the problem observed is present.
Comment 2 IBM Bug Proxy 2017-04-19 18:00:18 UTC 
------- Comment From ruddk.com 2017-04-19 13:58 EDT-------
(In reply to comment #4)
...
> Additional info:
> Note, the issue was originally noted at installation-time as the default
> superblock format for PPC64 (PReP boot) systems is 1.0 according to the
> python-blivet library, used by the anaconda installer, code snippet below:
>
> def preCommitFixup(self, *args, **kwargs):
> """ Determine create parameters for this set """
> mountpoints = kwargs.pop("mountpoints")
> log_method_call(self, self.name, mountpoints)
>
> if "/boot" in mountpoints:
> bootmountpoint = "/boot"
> else:
> bootmountpoint = "/"
>
> # If we are used to boot from we cannot use 1.1 metadata
> if getattr(self.format, "mountpoint", None) == bootmountpoint or \
> getattr(self.format, "mountpoint", None) == "/boot/efi" or \
> self.format.type == "prepboot":
> self.metadataVersion = "1.0"

This is probably the key observation.  It doesn't really make sense to have this restriction in place for disks with a PReP partition.  The above appears to have already been backed out via the following commit:

commit 8bce84025e0f0af9b2538a2611e5d52257a82881
Author: David Lehman <dlehman>
Date:   Wed May 27 16:07:05 2015 -0500

Use the default md metadata version for everything except /boot/efi.

Now that we've moved to grub2 this is no longer necessary for /boot.
As far as I know we have never actually allowed PReP on md, so that's
not needed either. Apparently UEFI firmware/bootloader still needs it.

Related: rhbz#1061711
Comment 3 Hanns-Joachim Uhl 2017-04-23 08:19:23 UTC 
.
Comment 4 IBM Bug Proxy 2017-04-23 08:25:16 UTC 
------- Comment From cjt.com 2017-04-21 12:48 EDT-------
Here's where I have stopped grub2-install in gdb:

(gdb) run -vvv /dev/sda1
...
grub-core/osdep/hostdisk.c:415: opening the device `/dev/sda2' in open_device()
(gdb) bt
#0  grub_util_fd_seek (fd=0x8, off=0x3dcf8000) at grub-core/osdep/unix/hostdisk.c:105
#1  0x000000001013f3ac in grub_util_fd_open_device (disk=0x101e88e0, sector=0x3dcf8, flags=0x101000, max=0x3fffffffe018)
at grub-core/osdep/linux/hostdisk.c:450
#2  0x000000001013c56c in grub_util_biosdisk_read (disk=0x101e88e0, sector=0x404f8, size=0x8, buf=0x101ee130 "\370\016\347\267\377?")
at grub-core/kern/emu/hostdisk.c:289
#3  0x0000000010133ccc in grub_disk_read_small_real (disk=0x101e88e0, sector=0x2027c0, offset=0x6000, size=0x100, buf=0x3fffffffe308)
at grub-core/kern/disk.c:344
#4  0x0000000010133fac in grub_disk_read_small (disk=0x101e88e0, sector=0x2027c0, offset=0x6000, size=0x100, buf=0x3fffffffe308)
at grub-core/kern/disk.c:401
#5  0x00000000101341a8 in grub_disk_read (disk=0x101e88e0, sector=0x2027f0, offset=0x0, size=0x100, buf=0x3fffffffe308)
at grub-core/kern/disk.c:440
#6  0x000000001004371c in grub_mdraid_detect (disk=0x101e88e0, id=0x3fffffffe4c8, start_sector=0x3fffffffe4c0)
at grub-core/disk/mdraid1x_linux.c:149
#7  0x0000000010155eb0 in scan_disk_partition_iter (disk=0x101e88e0, p=0x3fffffffe548, data=0x101e8860) at grub-core/disk/diskfilter.c:161
#8  0x0000000010147000 in part_iterate (dsk=0x101e88e0, partition=0x3fffffffe660, data=0x3fffffffe900) at grub-core/kern/partition.c:196
#9  0x000000001015a2b8 in grub_partition_msdos_iterate (disk=0x101e88e0, hook=0x10146f24 <part_iterate>, hook_data=0x3fffffffe900)
at grub-core/partmap/msdos.c:196
#10 0x000000001014718c in grub_partition_iterate (disk=0x101e88e0, hook=0x10155ccc <scan_disk_partition_iter>, hook_data=0x101e8860)
at grub-core/kern/partition.c:233
#11 0x00000000101560c0 in scan_disk (name=0x101e8860 "hd0", accept_diskfilter=0x1) at grub-core/disk/diskfilter.c:204
#12 0x00000000101591ec in grub_diskfilter_get_pv_from_disk (disk=0x101e8810, vg_out=0x3fffffffea30) at grub-core/disk/diskfilter.c:1173
#13 0x0000000010154f9c in grub_util_get_ldm (disk=0x101e8810, start=0x2800) at grub-core/disk/ldm.c:876
#14 0x0000000010135bb0 in grub_util_biosdisk_get_grub_dev (os_dev=0x101e5fd0 "/dev/sda2") at util/getroot.c:437
#15 0x000000001013531c in grub_util_pull_device (os_dev=0x101e5fd0 "/dev/sda2") at util/getroot.c:111
#16 0x000000001013a6a0 in grub_util_pull_device_os (os_dev=0x101e7520 "/dev/md0", ab=GRUB_DEV_ABSTRACTION_RAID)
at grub-core/osdep/linux/getroot.c:1064
#17 0x0000000010135300 in grub_util_pull_device (os_dev=0x101e7520 "/dev/md0") at util/getroot.c:108
#18 0x0000000010006688 in main (argc=0x3, argv=0x3ffffffff528) at util/grub-install.c:1233
(gdb) frame 6
#6  0x000000001004371c in grub_mdraid_detect (disk=0x101e88e0, id=0x3fffffffe4c8, start_sector=0x3fffffffe4c0)
at grub-core/disk/mdraid1x_linux.c:149
149	      if (grub_disk_read (disk, sector, 0, sizeof (struct grub_raid_super_1x),
(gdb) print minor_version
$34 = 0x0
(gdb) print *((*disk)->partition)
$35 = {number = 0x1, start = 0x2800, len = 0x200000, offset = 0x0, index = 0x1, parent = 0x0, partmap = 0x101ba250 <grub_msdos_partition_map>,
msdostype = 0xfd}
(gdb) print sector
$36 = 0x1ffff0
(gdb) frame 0
#0  grub_util_fd_seek (fd=0x8, off=0x3dcf8000) at grub-core/osdep/unix/hostdisk.c:105
105	  if (lseek (fd, offset, SEEK_SET) != offset)
(gdb) print offset
$37 = 0x3dcf8000

There seem to be at least 1 problem with the sector/offset computations.  According to mdadm -E /dev/sda2:

Super Offset : 2097136 sectors
(that's 512b sectors because my partition is only 1GB)
Therefore we find our md superblock at 0x3FFFE.

I believe one problem is in grub_util_fd_open_device().  It is passed sector=404f8, which refers to 4096b sectors.  grub_util_fd_open_device() then subtracts the part_start which comes from disk->partition->start=0x2800 in grub_partition_get_start().  But that 0x2800 refers to 512b sectors.

Here is the partition table:
Model: AIX VDASD (scsi)
Disk /dev/sda: 5242880s
Sector size (logical/physical): 4096B/4096B
Partition Table: msdos
Disk Flags:

Number  Start    End       Size      Type     File system  Flags
1      256s     1279s     1024s     primary               boot, prep
2      1280s    263423s   262144s   primary               raid
3      263424s  4451327s  4187904s  primary               raid

Partition 2 starts at 1280s (based on 4096b sectors) which is 0x500s.
(gdb) frame 6
#6  0x000000001004371c in grub_mdraid_detect (disk=0x101e88e0, id=0x3fffffffe4c8, start_sector=0x3fffffffe4c0)
at grub-core/disk/mdraid1x_linux.c:149
149	      if (grub_disk_read (disk, sector, 0, sizeof (struct grub_raid_super_1x),
(gdb) print ((*disk)->partition)->start
$42 = 0x2800

So grub_util_fd_open() mixed the native 4096b sectors with the grub sector size of 512b. sector=0x404f8 was passed in but the mixing of sector sizes caused the offset sent to grub_util_fd_seek to be 0x3dcf8000 instead of 0x3FFF8000.

------- Comment From ruddk.com 2017-04-21 12:57 EDT-------
Just to clarify for others in case the "All" arch specification in this bug is missed: This isn't really PPC64* specfic.  The problem can be easily reproduced in an x86_64 KVM guest environment by simply presenting one of the virtual disks as a 4096 block device.  For example:

<disk type='block' device='disk'>
<driver name='qemu' type='raw' cache='none'/>
<source dev='/dev/vg_root/spare'/>
<blockio logical_block_size='4096' physical_block_size='4096'/>
<target dev='vdb' bus='virtio'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x08' function='0x0'/>
</disk>
Comment 5 IBM Bug Proxy 2017-06-08 18:00:22 UTC 
------- Comment From willianr.com 2017-06-08 13:55 EDT-------
I just ran a fresh installation enabling raid on a 4k block disk and I could not reproduce the problem stated on additional notes "the issue was originally noted at installation-time". Here are the information right after the first boot:

[root@rhel-grub ~]# uname -a
Linux rhel-grub 3.10.0-514.el7.ppc64le #1 SMP Wed Oct 19 11:27:06 EDT 2016 ppc64le ppc64le ppc64le GNU/Linux

[root@rhel-grub ~]# cat /etc/redhat-release
Red Hat Enterprise Linux Server release 7.3 (Maipo)

[root@rhel-grub ~]# df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/md126      9.0G  1.2G  7.9G  13% /
devtmpfs        8.0G     0  8.0G   0% /dev
tmpfs           8.0G     0  8.0G   0% /dev/shm
tmpfs           8.0G   14M  8.0G   1% /run
tmpfs           8.0G     0  8.0G   0% /sys/fs/cgroup
/dev/md127     1018M  145M  874M  15% /boot
tmpfs           1.6G     0  1.6G   0% /run/user/0

[root@rhel-grub ~]# cat /proc/mdstat
md126 : active raid1 sdb1[1] sda2[0]
9423872 blocks super 1.2 [2/2] [UU]
bitmap: 1/1 pages [64KB], 65536KB chunk

md127 : active raid1 sdb2[1] sda3[0]
1048512 blocks super 1.0 [2/2] [UU]
bitmap: 0/1 pages [0KB], 65536KB chunk

[root@rhel-grub ~]# grub2-probe --device /dev/md126 --target fs_uuid
5de99add-1cf2-41f0-ba54-c08067e404d4

[root@rhel-grub ~]# grub2-probe --device /dev/md127 --target fs_uuid
d48f8f83-717b-405e-9e7b-02ba37de959a

[root@rhel-grub ~]# parted /dev/sda u s p
Model: QEMU QEMU HARDDISK (scsi)
Disk /dev/sda: 2621440s
Sector size (logical/physical): 4096B/4096B
Partition Table: msdos
Disk Flags:

Number  Start     End       Size      Type     File system  Flags
1      256s      1279s     1024s     primary               boot, prep
2      1280s     2359295s  2358016s  primary               raid
3      2359296s  2621439s  262144s   primary               raid

[root@rhel-grub ~]# parted /dev/sdb u s p
Model: QEMU QEMU HARDDISK (scsi)
Disk /dev/sdb: 2621440s
Sector size (logical/physical): 4096B/4096B
Partition Table: msdos
Disk Flags:

Number  Start     End       Size      Type     File system  Flags
1      256s      2358271s  2358016s  primary               raid
2      2358272s  2620415s  262144s   primary               raid

I will do another installation without raid and then migrate it to raid to check if the problem happens.

So, for now, can someone confirm this problem happens during install time?
Comment 6 IBM Bug Proxy 2017-06-12 21:40:19 UTC 
------- Comment From willianr.com 2017-06-12 17:33 EDT-------
As expected, migrating /boot to raid 1 using metadata 1.0 when it is the first partition after prep fails:

[root@rhel-grub2-1 ~]# mdadm -D /dev/md0
/dev/md0:
Version : 1.0
Creation Time : Mon Jun 12 17:22:07 2017
Raid Level : raid1
Array Size : 1048512 (1023.94 MiB 1073.68 MB)
Used Dev Size : 1048512 (1023.94 MiB 1073.68 MB)
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent

Update Time : Mon Jun 12 17:26:45 2017
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0

Name : rhel-grub2-1:0  (local to host rhel-grub2-1)
UUID : 537bfbf4:0b89fb58:f50f14c3:ba5f2bf3
Events : 33

Number   Major   Minor   RaidDevice State
2     253        2        0      active sync   /dev/vda2
1     253       17        1      active sync   /dev/vdb1

[root@rhel-grub2-1 ~]# parted /dev/vda u s p
Model: Virtio Block Device (virtblk)
Disk /dev/vda: 2621440s
Sector size (logical/physical): 4096B/4096B
Partition Table: msdos
Disk Flags:

Number  Start    End       Size      Type     File system  Flags
1      256s     1279s     1024s     primary               boot, prep
2      1280s    263423s   262144s   primary               raid
3      263424s  2360575s  2097152s  primary

[root@rhel-grub2-1 ~]# parted /dev/vdb u s p
Model: Virtio Block Device (virtblk)
Disk /dev/vdb: 2621440s
Sector size (logical/physical): 4096B/4096B
Partition Table: msdos
Disk Flags:

Number  Start  End      Size     Type     File system  Flags
1      256s   262399s  262144s  primary               raid

[root@rhel-grub2-1 ~]# grub2-probe --device /dev/md0 --target fs_uuid
grub2-probe: error: disk ?mduuid/537bfbf40b89fb58f50f14c3ba5f2bf3? not found.

[root@rhel-grub2-1 ~]# grub2-install /dev/vdb
Installing for powerpc-ieee1275 platform.
grub2-install: error: disk ?mduuid/537bfbf40b89fb58f50f14c3ba5f2bf3? not found.

Now, interesting thing is that I was not able to migrate /boot to raid 1 using metadata 1.0 when /boot is not the first partition after prep (just like the installer did on comment #15). When I tried the same as the installer did, grub was not able to find /boot partition after root partition.
Comment 7 IBM Bug Proxy 2017-09-26 12:10:21 UTC 
------- Comment From victora.com 2017-09-26 08:09 EDT-------
Hi,

I still didn't have time to work on this. I will try to work on this bz this week.
I will let you know when I have updates.

Thanks
Victor
Comment 8 Chris Coates 2017-10-27 11:32:30 UTC 
Is there any progress on this?

We've just been hit by the same issue on an E850 during install, getting to the point where we can't install a system using software RAID 1.

As it stands, we're having to install without RAID to get a system up and running...
Comment 9 IBM Bug Proxy 2017-10-27 15:01:01 UTC 
------- Comment From ruddk.com 2017-10-27 10:51 EDT-------
(In reply to comment #23)
> Is there any progress on this?
>
> We've just been hit by the same issue on an E850 during install, getting to
> the point where we can't install a system using software RAID 1.
>
> As it stands, we're having to install without RAID to get a system up and
> running...

The install-side issue should already have been addressed for RHEL 7.4 via RH Bug 1184945.  The easy workaround is to not  use version 1.0 metadata for the RAID config.
Comment 10 Chris Coates 2017-10-27 16:14:52 UTC 
(In reply to IBM Bug Proxy from comment #9)
> ------- Comment From ruddk.com 2017-10-27 10:51 EDT-------
> (In reply to comment #23)
> > Is there any progress on this?
> >
> > We've just been hit by the same issue on an E850 during install, getting to
> > the point where we can't install a system using software RAID 1.
> >
> > As it stands, we're having to install without RAID to get a system up and
> > running...
> 
> The install-side issue should already have been addressed for RHEL 7.4 via
> RH Bug 1184945.  The easy workaround is to not  use version 1.0 metadata for
> the RAID config.

Unfortunately you can't specify a metadata type via kickstart for md devices - so that's still a show-stopper for using RHEL7.3 on an E850.

As a work-around to allow RAID during install, i've had to specify /boot as a btrfs partition, which worked perfectly fine.

Still - this isn't exactly an ideal solution for anyone using an E850 with RHEL 7.3... The customer i'm building out for isn't prepared to use RHEL 7.4 yet.
Comment 11 IBM Bug Proxy 2017-10-27 17:30:22 UTC 
------- Comment From desnesn.com 2017-10-27 13:23 EDT-------
Hello Kevin,

The engineer that was in charged of this Bug is leaving IBM.

I am working in this bug as we speak (started this week), and I think I am up to something. I will post my results by the end of the day.
Comment 12 IBM Bug Proxy 2017-10-27 21:00:27 UTC 
------- Comment From desnesn.com 2017-10-27 16:59 EDT-------
For now, I tried to look inside grub-probe to see if I could find any clues.

Through gdb, I noticed that when using 4k blocksize with --metadata=1.0 on the MD Raid disks, the `dev` variable from util/grub-probe.c +376 is coming out not allocated, so a grub_util_error() is being thrown.

============================
util/grub-probe.c +376
============================
376 dev = grub_device_open (drives_names[0]);
377 if (! dev)
378 	grub_util_error ("%s", grub_errmsg);
============================

Now, comparing grub_device_open() code on grub-core/kern/device.c, and using both --metadata=1.0 and --metadata=0.90:

============================
grub-core/kern/device.c +47
============================
47 dev = grub_malloc (sizeof (*dev));
48 if (! dev)
49 	goto fail;
50
51 dev->net = NULL;
52 /* Try to open a disk.  */
53 dev->disk = grub_disk_open (name);
54 if (dev->disk)
55	return dev;
56 if (grub_net_open && grub_errno == GRUB_ERR_UNKNOWN_DEVICE)
57 {
58 	grub_errno = GRUB_ERR_NONE;
59 	dev->net = grub_net_open (name);
60 }
61
62 if (dev->net)
63 	return dev;
64
65 fail:
66 	grub_free (dev);
============================

CURIOSITY: The addresses that came out of the grub_malloc() on line 47 seem a bit odd with 1.0.

=====
RAID using --metadata=1.0: FAILS on grub2-probe
=====
Breakpoint 4, grub_device_open (name=0x10185290 "mduuid/ceebb143b7f740ba41794f2e88b1e1de") at grub-core/kern/device.c:48
48	  if (! dev)
(gdb) print *dev
$3 = {
disk = 0x0,
net = 0x3fffb7ed07b8 <main_arena+104>
}

(gdb) print *dev->net
$4 = {
server = 0x3fffb7ed07a8 <main_arena+88> "\240(\034\020",
name = 0x3fffb7ed07a8 <main_arena+88> "\240(\034\020",
protocol = 0x3fffb7ed07b8 <main_arena+104>,
packs = {
first = 0x3fffb7ed07b8 <main_arena+104>,
last = 0x3fffb7ed07c8 <main_arena+120>,
count = 70367534974920
},
offset = 70367534974936,
fs = 0x3fffb7ed07d8 <main_arena+136>,
eof = -1209202712,
stall = 16383
}
=====

=====
RAID using --metadata=0.90: SUCCESS on grub2-probe
=====
Breakpoint 2, grub_device_open (name=0x10185830 "mduuid/1940b3311771bbb17b777c24c48ad94b") at grub-core/kern/device.c:48
48	  if (! dev)
(gdb) print *dev
$1 = {
disk = 0x0,
net = 0x10185120
}

(gdb) print *dev->net
$3 = {
server = 0x61 <Address 0x61 out of bounds>,
name = 0x21 <Address 0x21 out of bounds>,
protocol = 0x3fffb7ed07b8 <main_arena+104>,
packs = {
first = 0x3fffb7ed07b8 <main_arena+104>,
last = 0x20,
count = 32
},
offset = 7742648064551382888,
fs = 0x64762f7665642f2f,
eof = 98,
stall = 0
}
=====

Anyhow, this was only an allocation, and on line 51 of grub-core/kern/device.c dev->net receives NULL.

Using --metadata=1.0, `dev` is allocated, and the execution moves into grub_disk_open() on line 53. This function is returning a struct with its value set to zero here. Thus, it will jump the ifs on lines 54, 56 and 62; and eventually fails on 65.

=====
RAID using --metadata=1.0: FAILS on grub2-probe
=====
Breakpoint 2, grub_device_open (name=0x10185290 "mduuid/7266eba408736585cf9c00e3a2342fdc") at grub-core/kern/device.c:54
54	  if (dev->disk)
(gdb) print *dev
$3 = {
disk = 0x0,
net = 0x0
}
=====

Whereas using --metadata=0.90, the struct is not zeroed out, and grub_device_open() returns `dev` on line 54.

=====
RAID using --metadata=0.90: SUCCESS on grub2-probe
=====
Breakpoint 1, grub_device_open (name=0x10185830 "mduuid/a29da500c684c0d47b777c24c48ad94b") at grub-core/kern/device.c:54
54	  if (dev->disk)
(gdb) print *dev
$1 = {
disk = 0x101834a0,
net = 0x0
}
=====

Riddle me this: why?

More grub to come ... will look into grub_disk_open() and on mdadm next.
Comment 13 IBM Bug Proxy 2017-10-31 13:50:35 UTC 
------- Comment From desnesn.com 2017-10-31 09:49 EDT-------
Going deeper in the rabbit hole from IBM Comment 27 / RH Comment 12:

============================
grub-core/kern/disk.c +187
============================
187 grub_disk_t
188 grub_disk_open (const char *name)
189 {
...
224 for (dev = grub_disk_dev_list; dev; dev = dev->next)
225 {
226 	if ((dev->open) (raw, disk) == GRUB_ERR_NONE)
227 		break;
228 	else if (grub_errno == GRUB_ERR_UNKNOWN_DEVICE)
229 		grub_errno = GRUB_ERR_NONE;
230 	else
231 	goto fail;
232 }
233
234 if (! dev)
235 {
236 grub_error (GRUB_ERR_UNKNOWN_DEVICE, N_("disk `%s' not found"),
237          name);
238 goto fail;
239 }
============================

Using --metadata=1.0, `dev` comes zeroed out after the for loop on line 224, whereas on 0.90 it is defined. Moreover, line 236 grub_error() message is the one being printed by grub2-probe.

=====
FAILURE grub2-probe - RAID using --metadata=1.0
=====
Breakpoint 1, grub_disk_open (name=0x10185290 "mduuid/0ef5c3920edae097657894d84aef753d") at grub-core/kern/disk.c:234
234	  if (! dev)
(gdb) print dev
$1 = (grub_disk_dev_t) 0x0
(gdb) print *dev
Cannot access memory at address 0x0
(gdb) s
236	      grub_error (GRUB_ERR_UNKNOWN_DEVICE, N_("disk `%s' not found"),
=====

=====
SUCCESS grub2-probe - RAID using --metadata=0.90
=====
Breakpoint 1, grub_disk_open (name=0x10185830 "mduuid/ebae38d5105eed037b777c24c48ad94b") at grub-core/kern/disk.c:234
234	  if (! dev)
(gdb) print dev
$1 = (grub_disk_dev_t) 0x10165e80 <grub_diskfilter_dev>
(gdb) print *dev
$2 = {
name = 0x10146d50 "diskfilter",
id = GRUB_DISK_DEVICE_DISKFILTER_ID,
iterate = 0x101107cc <grub_diskfilter_iterate>,
open = 0x10110fd8 <grub_diskfilter_open>,
close = 0x10111120 <grub_diskfilter_close>,
read = 0x1011220c <grub_diskfilter_read>,
write = 0x1011227c <grub_diskfilter_write>,
memberlist = 0x10110950 <grub_diskfilter_memberlist>,
raidname = 0x10110df4 <grub_diskfilter_getname>,
next = 0x10165fb8 <grub_procfs_dev>
}
(gdb) s
240	  if (disk->log_sector_size > GRUB_DISK_CACHE_BITS + GRUB_DISK_SECTOR_BITS
=====

Since `dev` is used for a couple of devices on grub and this is a C template struct, each dev had its own functions. In our case, we are dealing with grub_disk_dev_t, and through gdb we can see that dev->open() on line 226 actually is grub_diskfilter_open() on:

============================
grub-core/disk/diskfilter.c +419
============================
419 static grub_err_t
420 grub_diskfilter_open (const char *name, grub_disk_t disk)
421 {
422   struct grub_diskfilter_lv *lv;
423
424   if (!is_valid_diskfilter_name (name))
425      return grub_error (GRUB_ERR_UNKNOWN_DEVICE, "unknown DISKFILTER device %s",
426                         name);
427
428   lv = find_lv (name);
429
430   if (! lv)
431     {
432       scan_devices (name);
433       if (grub_errno)
434         {
435           grub_print_error ();
436           grub_errno = GRUB_ERR_NONE;
437         }
438       lv = find_lv (name);
439     }
440
441   if (!lv)
442     return grub_error (GRUB_ERR_UNKNOWN_DEVICE, "unknown DISKFILTER device %s",
443                        name);
444
445   disk->id = lv->number;
446   disk->data = lv;
447
448   disk->total_sectors = lv->size;
449   disk->max_agglomerate = GRUB_DISK_MAX_MAX_AGGLOMERATE;
450   return 0;
============================

The is_valid_diskfilter_name() check on line 426 passes for both metadatas 0.90 and 1.0.

However, if we break line 441, a strange thing to note here - using --metadata=1.0 all my disk devices passes through the breakpoint, whereas using 0.90 only the raid device passed through the breakpoint on line 441.

=====
FAILURE grub2-probe - RAID using --metadata=1.0
=====
Breakpoint 1, grub_diskfilter_open (name=0x10185b90 "lvm/rhel-root", disk=0x101827d0) at grub-core/disk/diskfilter.c:441
441	  if (!lv)
(gdb) c
Continuing.

Breakpoint 1, grub_diskfilter_open (name=0x101859f0 "lvm/rhel-home", disk=0x101827d0) at grub-core/disk/diskfilter.c:441
441	  if (!lv)
(gdb) c
Continuing.

Breakpoint 1, grub_diskfilter_open (name=0x101857e0 "lvm/rhel-swap", disk=0x101827d0) at grub-core/disk/diskfilter.c:441
441	  if (!lv)
(gdb) c
Continuing.

...

Breakpoint 2, grub_diskfilter_open (name=0x10185290 "mduuid/0ef5c3920edae097657894d84aef753d", disk=0x10182780) at grub-core/disk/diskfilter.c:441
441	  if (!lv)
(gdb) print lv
$2 = (struct grub_diskfilter_lv *) 0x0
(gdb) print *lv
Cannot access memory at address 0x0
(gdb) s
442	    return grub_error (GRUB_ERR_UNKNOWN_DEVICE, "unknown DISKFILTER device %s",
=====

=====
SUCCESS grub2-probe - RAID using --metadata=0.90
=====
Breakpoint 1, grub_diskfilter_open (name=0x10185830 "mduuid/c5e0adca3d6a76ef7b777c24c48ad94b", disk=0x101834a0) at grub-core/disk/diskfilter.c:441
441	  if (!lv)
(gdb) print lv
$1 = (struct grub_diskfilter_lv *) 0x10183690
(gdb) print *lv
$2 = {
fullname = 0x10183580 "md/md1",
idname = 0x10183700 "mduuid/c5e0adca3d6a76ef7b777c24c48ad94b",
name = 0x10183580 "md/md1",
number = 0,
segment_count = 1,
segment_alloc = 0,
size = 20969344,
became_readable_at = 1,
scanned = 0,
visible = 1,
segments = 0x10183730,
vg = 0x10183530,
next = 0x0,
internal_id = 0x0
}
(gdb) s
445	  disk->id = lv->number;
=====

So, `lv` on 441 is coming out zeroed out. Let's back up a bit and break line 430:

=====
FAILURE grub2-probe - RAID using --metadata=1.0
=====
Breakpoint 2, grub_diskfilter_open (name=0x10185290 "mduuid/2872dd311d2585e4690defc1d9ba07a7", disk=0x10182780) at grub-core/disk/diskfilter.c:430
430	  if (! lv)
(gdb) print lv
$2 = (struct grub_diskfilter_lv *) 0x0
(gdb) print *lv
Cannot access memory at address 0x0
(gdb) c
Continuing.

...

Breakpoint 2, grub_diskfilter_open (name=0x10185b90 "lvm/rhel-root", disk=0x101827d0) at grub-core/disk/diskfilter.c:430
430	  if (! lv)
(gdb) c
Continuing.

Breakpoint 2, grub_diskfilter_open (name=0x101859f0 "lvm/rhel-home", disk=0x101827d0) at grub-core/disk/diskfilter.c:430
430	  if (! lv)
(gdb) c
Continuing.

Breakpoint 2, grub_diskfilter_open (name=0x101857e0 "lvm/rhel-swap", disk=0x101827d0) at grub-core/disk/diskfilter.c:430
430	  if (! lv)
(gdb) c
Continuing.
/usr/sbin/grub2-probe: error: disk ?mduuid/2872dd311d2585e4690defc1d9ba07a7? not found.
[Inferior 1 (process 19832) exited with code 01]
=====

=====
SUCCESS grub2-probe - RAID using --metadata=0.90
=====
Breakpoint 1, grub_diskfilter_open (name=0x10185830 "mduuid/a2f06ca0ad6cedbc7b777c24c48ad94b", disk=0x101834a0) at grub-core/disk/diskfilter.c:430
430	  if (! lv)
(gdb) print lv
$1 = (struct grub_diskfilter_lv *) 0x10183690
(gdb) print *lv
$2 = {
fullname = 0x10183580 "md/md1",
idname = 0x10183700 "mduuid/a2f06ca0ad6cedbc7b777c24c48ad94b",
name = 0x10183580 "md/md1",
number = 0,
segment_count = 1,
segment_alloc = 0,
size = 20969344,
became_readable_at = 1,
scanned = 0,
visible = 1,
segments = 0x10183730,
vg = 0x10183530,
next = 0x0,
internal_id = 0x0
}
=====

Thus, apparently the culprit now might be hiding on find_lv ().

============================
grub-core/disk/diskfilter.c +401
============================
401 static struct grub_diskfilter_lv *
402 find_lv (const char *name)
403 {
404   struct grub_diskfilter_vg *vg;
405   struct grub_diskfilter_lv *lv = NULL;
406
407   for (vg = array_list; vg; vg = vg->next)
408     {
409       if (vg->lvs)
410         for (lv = vg->lvs; lv; lv = lv->next)
411           if (((lv->fullname && grub_strcmp (lv->fullname, name) == 0)
412                || (lv->idname && grub_strcmp (lv->idname, name) == 0))
413               && is_lv_readable (lv, 0))
414             return lv;
415     }
416   return NULL;
417 }
============================

=====
FAILURE grub2-probe - RAID using --metadata=1.0
=====
Breakpoint 1, find_lv (name=0x10185290 "mduuid/e5cf979ce818f58cc57b618bd78b4b86") at grub-core/disk/diskfilter.c:407
407	  for (vg = array_list; vg; vg = vg->next)
(gdb) print array_list
$1 = (struct grub_diskfilter_vg *) 0x0
(gdb) print *array_list
Cannot access memory at address 0x0
(gdb) s
416	  return NULL;
=====

=====
SUCCESS grub2-probe - RAID using --metadata=0.90
=====
Breakpoint 5, find_lv (name=0x10185830 "mduuid/a2f06ca0ad6cedbc7b777c24c48ad94b") at grub-core/disk/diskfilter.c:407
407	  for (vg = array_list; vg; vg = vg->next)
(gdb) print array_list
$5 = (struct grub_diskfilter_vg *) 0x10183530
(gdb) print *array_list
$6 = {
uuid = 0x10183300 "\242\360l\240\255l\355\274{w|$?\331Ke/en_US.!",
uuid_len = 16,
name = 0x10183580 "md/md1",
extent_size = 1,
pvs = 0x10186090,
lvs = 0x10183690,
next = 0x0,
driver = 0x10160228 <grub_mdraid_dev>
}
(gdb) s
409	      if (vg->lvs)
=====

Therefore, at this point we can infer that RAID 1 with --metadata=1.0 on 4k blocksize disks is leading to the creation of an empty array_list, which is leading to everything else.

Riddle me this: why?

More gdb to come ... apparently array_list is being populated on grub_diskfilter_vg_register() at grub-core/disk/diskfilter.c +838.

Will look into that next, and eventually on mdadm.
Comment 14 IBM Bug Proxy 2017-12-11 20:31:04 UTC 
------- Comment From desnesn.com 2017-12-11 15:28 EDT-------
Finally had quality time for this bug again. Carrying on:

From breaking grub_diskfilter_vg_register(), we can observe that the disk is being registered differently on 1.0 to 0.90; and that is because the diskfilter that is being registered is for my rhel OS instead of my raid. By doing a backtrace, I also noticed that even the stack is different when calling grub_diskfilter_vg_register():

=====
--- bad     2017-12-07 13:44:39.654222238 -0200
+++ good    2017-12-07 13:43:52.563919187 -0200
@@ -1,36 +1,39 @@
-Breakpoint 1, grub_diskfilter_vg_register (vg=0x10185ea0) at grub-core/disk/diskfilter.c:849
+Breakpoint 1, grub_diskfilter_vg_register (vg=0x10183530) at grub-core/disk/diskfilter.c:849
849      for (lv = vg->lvs; lv; lv = lv->next)
(gdb) print *vg
$4 = {
-  uuid = 0x10185ef0 "xZL9PN-dXgE-Vflt-rtI5-Y203-gQ6e-TBS0Mz",
-  uuid_len = 38,
-  name = 0x10185e80 "rhel",
-  extent_size = 8192,
-  pvs = 0x10185f20,
-  lvs = 0x10185b00,
+  uuid = 0x10183300 "?\300\263\362\242\326]\232\334\316r\364\264\370\267e/en_US.!",
+  uuid_len = 16,
+  name = 0x10183580 "md/1",
+  extent_size = 1,
+  pvs = 0x101850c0,
+  lvs = 0x10183690,
next = 0x0,
driver = 0x0
}
(gdb) bt
-#0  grub_diskfilter_vg_register (vg=0x10185ea0) at grub-core/disk/diskfilter.c:849
-#1  0x0000000010009810 in grub_lvm_detect (disk=0x101827d0, id=0x3ffffffde4e8, start_sector=0x3ffffffde4e0) at grub-core/disk/lvm.c:744
-#2  0x00000000101102b0 in scan_disk_partition_iter (disk=0x101827d0, p=0x3ffffffde568, data=0x101812d0) at grub-core/disk/diskfilter.c:161
-#3  0x0000000010101400 in part_iterate (dsk=0x101827d0, partition=0x3ffffffde680, data=0x3ffffffde920) at grub-core/kern/partition.c:196
-#4  0x00000000101146b8 in grub_partition_msdos_iterate (disk=0x101827d0, hook=0x10101324 <part_iterate>, hook_data=0x3ffffffde920)
+#0  grub_diskfilter_vg_register (vg=0x10183530) at grub-core/disk/diskfilter.c:849

==> +#1  0x0000000010112dd0 in grub_diskfilter_make_raid (uuidlen=16,

+    uuid=0x10183300 "?\300\263\362\242\326]\232\334\316r\364\264\370\267e/en_US.!", nmemb=2, name=0x3ffffffde3e8 "rhel-7.3:1",
+    disk_size=20969216, stripe_size=0, layout=0, level=1) at grub-core/disk/diskfilter.c:1030
+#2  0x000000001000a414 in grub_mdraid_detect (disk=0x101834a0, id=0x3ffffffde588, start_sector=0x3ffffffde580)
+    at grub-core/disk/mdraid1x_linux.c:202
+#3  0x00000000101102b0 in scan_disk_partition_iter (disk=0x101834a0, p=0x3ffffffde608, data=0x10182800) at grub-core/disk/diskfilter.c:161
+#4  0x0000000010101400 in part_iterate (dsk=0x101834a0, partition=0x3ffffffde720, data=0x3ffffffde9c0) at grub-core/kern/partition.c:196
+#5  0x00000000101146b8 in grub_partition_msdos_iterate (disk=0x101834a0, hook=0x10101324 <part_iterate>, hook_data=0x3ffffffde9c0)
at grub-core/partmap/msdos.c:196
-#5  0x000000001010158c in grub_partition_iterate (disk=0x101827d0, hook=0x101100cc <scan_disk_partition_iter>, hook_data=0x101812d0)
+#6  0x000000001010158c in grub_partition_iterate (disk=0x101834a0, hook=0x101100cc <scan_disk_partition_iter>, hook_data=0x10182800)
at grub-core/kern/partition.c:233
-#6  0x00000000101104c0 in scan_disk (name=0x101812d0 "hd0", accept_diskfilter=0) at grub-core/disk/diskfilter.c:204
-#7  0x000000001011054c in scan_disk_hook (name=0x101812d0 "hd0", data=0x0) at grub-core/disk/diskfilter.c:213
-#8  0x00000000100f62e8 in grub_util_biosdisk_iterate (hook=0x1011051c <scan_disk_hook>, hook_data=0x0, pull=GRUB_DISK_PULL_NONE)
-    at grub-core/kern/emu/hostdisk.c:119
-#9  0x0000000010110610 in scan_devices (arname=0x10185290 "mduuid/76da2b4aea5de03cfc91176e98fc2140") at grub-core/disk/diskfilter.c:231
-#10 0x0000000010111050 in grub_diskfilter_open (name=0x10185290 "mduuid/76da2b4aea5de03cfc91176e98fc2140", disk=0x10182780)
-    at grub-core/disk/diskfilter.c:432
-#11 0x00000000100ee00c in grub_disk_open (name=0x10185290 "mduuid/76da2b4aea5de03cfc91176e98fc2140") at grub-core/kern/disk.c:226
-#12 0x00000000100ed0a0 in grub_device_open (name=0x10185290 "mduuid/76da2b4aea5de03cfc91176e98fc2140") at grub-core/kern/device.c:53
-#13 0x0000000010003ee0 in probe (path=0x0, device_names=0x10181050, delim=10 '\n') at util/grub-probe.c:376
-#14 0x00000000100056b4 in main (argc=5, argv=0x3ffffffff3d8) at util/grub-probe.c:882
+#7  0x00000000101104c0 in scan_disk (name=0x10182800 "hostdisk//dev/vda", accept_diskfilter=1) at grub-core/disk/diskfilter.c:204
+#8  0x00000000101135ec in grub_diskfilter_get_pv_from_disk (disk=0x101827b0, vg_out=0x3ffffffdeaf0) at grub-core/disk/diskfilter.c:1173
+#9  0x000000001010f39c in grub_util_get_ldm (disk=0x101827b0, start=2048) at grub-core/disk/ldm.c:876
+#10 0x00000000100f03f4 in grub_util_biosdisk_get_grub_dev (os_dev=0x1018a800 "/dev/vda1") at util/getroot.c:437
+#11 0x00000000100efb60 in grub_util_pull_device (os_dev=0x1018a800 "/dev/vda1") at util/getroot.c:111
+#12 0x00000000100f4ee4 in grub_util_pull_device_os (os_dev=0x10181350 "/dev/md1", ab=GRUB_DEV_ABSTRACTION_RAID)
+    at grub-core/osdep/linux/getroot.c:1064
+#13 0x00000000100efb44 in grub_util_pull_device (os_dev=0x10181350 "/dev/md1") at util/getroot.c:108
+#14 0x0000000010003b14 in probe (path=0x0, device_names=0x10181050, delim=10 '\n') at util/grub-probe.c:304
+#15 0x00000000100056b4 in main (argc=5, argv=0x3ffffffff3d8) at util/grub-probe.c:882
...
-/usr/sbin/grub2-probe: error: disk ?mduuid/76da2b4aea5de03cfc91176e98fc2140? not found.
-[Inferior 1 (process 17894) exited with code 01]
+d0aeef94-f2ba-4831-8bbe-523e587adc46
+[Inferior 1 (process 17933) exited normally]
=====

Since I also noticed that grub_diskfilter_make_raid() (grub-core/disk/mdraid_linux.c:256 for 0.90, and grub-core/disk/mdraid1x_linux.c:202 for 1.0) was never called when using 4k block size, I thought now would be interesting to change my testing and follow the good stack (512 block size) to see where the path deviates.

Thus, I decided to compare a raid disk of 4k (bad) with another of 512 (good), but only using only metadata 1.0 from this point on, which made me reach:

=====
--- bad        2017-11-29 23:27:37.127052665 -0200
+++ good       2017-11-29 23:24:12.039919190 -0200
...
Breakpoint 1, grub_mdraid_detect (disk=0x101834a0, id=0x3ffffffde9c8, start_sector=0x3ffffffde9c0) at grub-core/disk/mdraid1x_linux.c:153
153          if (sb.magic != grub_cpu_to_le32_compile_time (SB_MAGIC)
@@ -50,18 +50,21 @@ $18 = 0x8
(gdb) n
124      for (minor_version = 0; minor_version < 3; ++minor_version)
(gdb) print disk->name
-$19 = 0x101834f0 "hostdisk//dev/vdc"
+$19 = 0x101834f0 "hostdisk//dev/vda"
(gdb) c
Continuing.
...
(gdb) c
Continuing.
...
(gdb) c
Continuing.
...
Breakpoint 1, grub_mdraid_detect (disk=0x101834a0, id=0x3ffffffde588, start_sector=0x3ffffffde580) at grub-core/disk/mdraid1x_linux.c:153
153          if (sb.magic != grub_cpu_to_le32_compile_time (SB_MAGIC)
(gdb) p/x sb.magic
-$20 = 0x0
+$20 = 0xa92b4efc
(gdb) p/x sb.super_offset
-$21 = 0x0
+$21 = 0x13ff7f0
(gdb) p/x sector
$22 = 0x13ff7f0
(gdb) n
-155            continue;
+154              || grub_le_to_cpu64 (sb.super_offset) != sector)
+(gdb) n
+157          if (sb.major_version != grub_cpu_to_le32_compile_time (1))
...
and latter, grub_diskfilter_make_raid() was only called on the 512 raid.
Moreover, the next time this breakpoint is reached is for the other disk.
=====

Quick note:

=====
[root@rhel-7 grub-2.02~beta2]# grep -rnI "define SB_MAGIC" .
./grub-core/disk/mdraid1x_linux.c:32:#define SB_MAGIC                   0xa92b4efc
./grub-core/disk/mdraid_linux.c:97:#define SB_MAGIC                     0xa92b4efc
=====

Thus, the conditionals on line 153 and 157 are always falling since sb is zeroed out; never allowing grub_diskfilter_make_raid() to be called. The sb variable should had been filled in the line before:

============================
grub-core/disk/mdraid1x_linux.c
============================
149     if (grub_disk_read (disk, sector, 0, sizeof (struct grub_raid_super_1x),
150                            &sb))
151	    return NULL;
============================

Going deeper in the rabbit hole and skipping a few steps (inside grub_disk_read() at grub-core/kern/disk.c:413; which is a function that calls grub_disk_read_small() on grub-core/kern/disk.c:396; which calls grub_disk_read_small_real() at grub-core/kern/disk.c:317):

============================
grub-core/kern/disk.c
============================
380     if ((disk->dev->read) (disk, transform_sector (disk, aligned_sector),
381                            num, tmp_buf))
============================

We can observe that:

======
--- bad     2017-12-08 16:40:58.277936277 -0200
+++ good    2017-12-08 15:02:37.620925526 -0200
@@ -1,22 +1,22 @@
380        if ((disk->dev->read) (disk, transform_sector (disk, aligned_sector),
(gdb) p/x ((struct grub_raid_super_1x*) tmp_buf)->magic
-$11 = 0xb7ed0ec8
+$11 = 0xb7ed09a8
(gdb) p/x ((struct grub_raid_super_1x*) tmp_buf)->super_offset
$12 = 0x0
(gdb) p/x ((struct grub_raid_super_1x*) buf)->magic
$13 = 0x12
(gdb) p/x ((struct grub_raid_super_1x*) buf)->super_offset
$14 = 0x3ffffffde460
(gdb) n
-Detaching after fork from child process 19992.
+Detaching after fork from child process 19972.
389        grub_memcpy (buf, tmp_buf + offset, size);
(gdb) p/x ((struct grub_raid_super_1x*) tmp_buf)->magic
-$15 = 0x0
+$15 = 0xa92b4efc
(gdb) p/x ((struct grub_raid_super_1x*) tmp_buf)->super_offset
-$16 = 0x0
+$16 = 0x13ff7f0
(gdb) n
390        grub_free (tmp_buf);
(gdb) p/x ((struct grub_raid_super_1x*) buf)->magic
-$17 = 0x0
+$17 = 0xa92b4efc
(gdb) p/x ((struct grub_raid_super_1x*) buf)->super_offset
-$18 = 0x0
+$18 = 0x13ff7f0
======

Further, disk->dev->read() first calls transform_sector():

============================
grub-core/kern/disk_common.c
============================
42 static inline grub_disk_addr_t
43 transform_sector (grub_disk_t disk, grub_disk_addr_t sector)
44 {
45   return sector >> (disk->log_sector_size - GRUB_DISK_SECTOR_BITS);
46 }
============================

And aftewards disk->dev->read() (pointer to grub_util_biosdisk_read() on grub-core/kern/emu/hostdisk.c:282) calls grub_util_fd_read():

============================
grub-core/kern/emu/hostdisk.c
============================
281 static grub_err_t
282 grub_util_biosdisk_read (grub_disk_t disk, grub_disk_addr_t sector,
283                          grub_size_t size, char *buf)
284 {
...
305       if (grub_util_fd_read (fd, buf, max << disk->log_sector_size)
306           != (ssize_t) (max << disk->log_sector_size))
307         return grub_error (GRUB_ERR_READ_ERROR, N_("cannot read `%s': %s"),
308                            map[disk->id].device, grub_util_fd_strerror ());
============================

Which results:

======
--- bad     2017-12-08 17:21:19.963486041 -0200
+++ good    2017-12-08 17:21:18.714475999 -0200
@@ -1,17 +1,17 @@
305          if (grub_util_fd_read (fd, buf, max << disk->log_sector_size)
(gdb) p/x ((struct grub_raid_super_1x*) buf)->magic
-$18 = 0xb7ed0ec8
+$18 = 0xb7ed09a8
(gdb) p/x ((struct grub_raid_super_1x*) buf)->super_offset
$19 = 0x0
(gdb) p max << disk->log_sector_size
-$20 = 4096
+$20 = 512
(gdb) p/x sector
-$23 = 0x27fffe
+$23 = 0x13ffff0
(gdb) n
306              != (ssize_t) (max << disk->log_sector_size))
(gdb)
305          if (grub_util_fd_read (fd, buf, max << disk->log_sector_size)
(gdb) p/x ((struct grub_raid_super_1x*) buf)->magic
-$25 = 0x0
+$25 = 0xa92b4efc
(gdb) p/x ((struct grub_raid_super_1x*) buf)->super_offset
-$26 = 0x0
+$26 = 0x13ff7f0
======

Actually, the whole *buf is zeroed out after this call. Going inside grub_util_fd_read() now:

============================
grub-core/osdep/unix/hostdisk.c
============================
113 /* Read LEN bytes from FD in BUF. Return less than or equal to zero if an
114    error occurs, otherwise return LEN.  */
115 ssize_t
116 grub_util_fd_read (grub_util_fd_t fd, char *buf, size_t len)
117 {
118   ssize_t size = 0;
119
120   while (len)
121     {
122       ssize_t ret = read (fd, buf, len);
...
138     }
139
140   return size;
============================

Which led to:

======
--- bad     2017-12-08 18:42:33.937517190 -0200
+++ good    2017-12-08 18:39:08.588844344 -0200
@@ -1,16 +1,17 @@
-grub_util_fd_read (fd=8, buf=0x10184fd0 "\310\016\355\267\377?", len=4096) at grub-core/osdep/unix/hostdisk.c:118
+grub_util_fd_read (fd=8, buf=0x10183530 "\250\t\355\267\377?", len=512) at grub-core/osdep/unix/hostdisk.c:118
118      ssize_t size = 0;
(gdb) n
120      while (len)
(gdb)
122          ssize_t ret = read (fd, buf, len);
(gdb) p/x ((struct grub_raid_super_1x*) buf)->magic
-$31 = 0xb7ed0ec8
+$31 = 0xb7ed09a8
(gdb) p/x ((struct grub_raid_super_1x*) buf)->super_offset
$32 = 0x0
(gdb) n
124          if (ret == 0)
(gdb) p/x ((struct grub_raid_super_1x*) buf)->magic
-$35 = 0x0
+$35 = 0xa92b4efc
(gdb) p/x ((struct grub_raid_super_1x*) buf)->super_offset
-$36 = 0x0
+$36 = 0x13ff7f0
(gdb) p ret
-$37 = 4096
+$37 = 512
======

Note that 4096 zeroes were read, and that's why no error is thrown on grub-core/kern/emu/hostdisk.c:305.

Now the question is: are we reading on the wrong sector, or is this data really zeroed out (which would imply that the bug is on mdadm?)?

I believe we have enough data to start an upstream discussion, which I plan to do soon. More to come ...
Comment 15 IBM Bug Proxy 2018-01-16 19:10:44 UTC 
------- Comment From desnesn.com 2018-01-16 14:09 EDT-------
Just for the record, I have also reproduced this bug in x86_64 with ubuntu 17.10.
Comment 17 Peter Jones 2018-06-06 19:01:20 UTC 
This works for me using grub2-2.02-0.65.el7_4.2 on an EFI machine with a 4k disk:

[root@pjones3 tmp]# blockdev --getbsz /dev/sdb
4096
[root@pjones3 tmp]# blockdev --getbsz /dev/sdb2
4096
[root@pjones3 tmp]# blockdev --getbsz /dev/md0
4096
[root@pjones3 tmp]# ./usr/sbin/grub2-probe --target fs_uuid -d /dev/sdb2
c1b85a71-972d-4b69-84cc-e6a05326a4c8
[root@pjones3 tmp]# ./usr/sbin/grub2-probe --target fs_uuid -d /dev/md0
c1b85a71-972d-4b69-84cc-e6a05326a4c8

Note the detection in mdraid1x_linux.c still isn't right, because it's trying to find the raid superblock based on the location of the superblock data based on the size of /dev/sdb rather than /dev/sdb2, but grub2-probe and booting the machine with /boot on this raid are both successful.

I see this was reported with grub2-2.02-0.44.el7 ; does the newer package work for you?
Comment 18 IBM Bug Proxy 2018-06-13 19:30:21 UTC 
------- Comment From diegodo.com 2018-06-13 15:24 EDT-------
Hi, I'm still getting the result:

./grub-probe: error: disk `mduuid/b184ce73be4a91ec1b586dcce8ee7f9b' not found.

One thing that I noticed  is that we have some sector lengths hardcoded for 512 bytes. Yet, it seems that grub is facing some problems when trying to find magic number for 1.0 metadata.

I did dump the variables returned by the disk read when the mdraid1x_linux.c tries to find the magic number and its getting the wrong position.

When I finally changed the hardcoded sector lenghts for 4k instead, the mdraid1x_linux.c was able to find the magic number, although it wasn't able to   successful find the disk yet.

I'm still investigating this problem and hope I find something in a couple of days.

Thank you
Comment 21 Hanns-Joachim Uhl 2019-06-13 09:12:28 UTC 
ok ... with no news for this bugzilla since exactly one year
I am closing this Red Hat bugzilla now
and please reopen if required with then using the current RHEL7.7 ...
... thanks for your support ...
Comment 23 Konstantin Shalygin 2023-07-05 12:30:31 UTC 
This issue actually still exists on CentOS8-Stream, but we find workaround: the EFI partition should be not first


The workaround is:
```
ignoredisk --only-use=nvme0n1,nvme1n1
clearpart --none --initlabel
part raid.149 --fstype="mdmember" --ondisk=nvme1n1 --size=55895
part raid.156 --fstype="mdmember" --ondisk=nvme1n1 --size=250
part raid.142 --fstype="mdmember" --ondisk=nvme0n1 --size=250
part raid.135 --fstype="mdmember" --ondisk=nvme0n1 --size=55895
raid / --device=root --fstype="xfs" --level=RAID1 raid.135 raid.149
raid /boot/efi --device=boot_efi --fstype="efi" --level=RAID1 --fsoptions="umask=0077,shortname=winnt" raid.142 raid.156
```

System boot's fine:
```
[root@host]# lsblk
NAME        MAJ:MIN RM  SIZE RO TYPE  MOUNTPOINT
nvme2n1     259:0    0  3.7T  0 disk
nvme3n1     259:1    0  3.7T  0 disk
nvme0n1     259:2    0 54.9G  0 disk
|-nvme0n1p1 259:3    0 54.6G  0 part
| `-md127     9:127  0 54.6G  0 raid1 /
`-nvme0n1p2 259:4    0  250M  0 part
  `-md126     9:126  0  250M  0 raid1 /boot/efi
nvme1n1     259:5    0 54.9G  0 disk
|-nvme1n1p1 259:6    0 54.6G  0 part
| `-md127     9:127  0 54.6G  0 raid1 /
`-nvme1n1p2 259:7    0  250M  0 part
  `-md126     9:126  0  250M  0 raid1 /boot/efi
```

grub2-probes:
```
[root@host]# grub2-probe --target fs_uuid -d /dev/md126
0D55-B32D
[root@host]# grub2-probe --target fs_uuid -d /dev/md127
595b5582-06b2-444a-966f-f4e3bd52d74c
```

Fdisk:
```
[root@host]# fdisk -l | grep "Disk /dev" -A 2
Disk /dev/nvme2n1: 3.7 TiB, 4000787030016 bytes, 976754646 sectors
Units: sectors of 1 * 4096 = 4096 bytes
Sector size (logical/physical): 4096 bytes / 4096 bytes
--
Disk /dev/nvme3n1: 3.7 TiB, 4000787030016 bytes, 976754646 sectors
Units: sectors of 1 * 4096 = 4096 bytes
Sector size (logical/physical): 4096 bytes / 4096 bytes
--
Disk /dev/nvme0n1: 54.9 GiB, 58977157120 bytes, 14398720 sectors
Units: sectors of 1 * 4096 = 4096 bytes
Sector size (logical/physical): 4096 bytes / 4096 bytes
--
Disk /dev/nvme1n1: 54.9 GiB, 58977157120 bytes, 14398720 sectors
Units: sectors of 1 * 4096 = 4096 bytes
Sector size (logical/physical): 4096 bytes / 4096 bytes
--
Disk /dev/md127: 54.6 GiB, 58575552512 bytes, 14300672 sectors
Units: sectors of 1 * 4096 = 4096 bytes
Sector size (logical/physical): 4096 bytes / 4096 bytes
--
Disk /dev/md126: 250 MiB, 262078464 bytes, 63984 sectors
Units: sectors of 1 * 4096 = 4096 bytes
Sector size (logical/physical): 4096 bytes / 4096 bytes
```

packages versions:
grub2-common-2.02-129.el8.noarch
kernel-4.18.0-499.el8.x86_64

PR for anaconda docs "Common bugs and issues" [1]


[1] https://github.com/rhinstaller/anaconda/pull/4880
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