[linux-lvm] cache_check --clear-needs-check-flag does not clear needs_check flag?

[Dennis Schridde]

Hello!

A cached logical volume of mine cannot be activated anymore:

$ sudo vgchange -ay
   device-mapper: reload ioctl on   (253:6) failed: Invalid argument
   0 logical volume(s) in volume group "vg_ernie" now active


dmesg logs:

device-mapper: cache: 253:6: unable to switch cache to write mode until
repaired.
device-mapper: cache: 253:6: switching cache to read-only mode
device-mapper: table: 253:6: cache: Unable to get write access to metadata,
please check/repair metadata.
device-mapper: ioctl: error adding target to table


The code in question seems to be: https://github.com/torvalds/linux/blob/v5.8/
drivers/md/dm-cache-target.c#L957-L964


Hence I set out to check the cache and, if it is clean, clear the needs_check
flag:

$ sudo lvchange -ay vg_ernie/lv_cache
Do you want to activate component LV in read-only mode? [y/n]: y
   Allowing activation of component LV.

$ sudo cache_check /dev/vg_ernie/lv_cache
examining superblock
examining mapping array
examining hint array
examining discard bitset

$ sudo cache_check --clear-needs-check-flag /dev/vg_ernie/lv_cache
examining superblock
examining mapping array
examining hint array
examining discard bitset

$ sudo lvchange -an vg_ernie/lv_cache


But the problem persists:

$ sudo vgchange -ay
   device-mapper: reload ioctl on   (253:6) failed: Invalid argument
   0 logical volume(s) in volume group "vg_ernie" now active


I tried again in read/write mode, in case that would make a difference /
silently fail:

$ sudo lvchange -ay vg_ernie/lv_cache
Do you want to activate component LV in read-only mode? [y/n]: n

$ sudo cache_check --clear-needs-check-flag /dev/vg_ernie/lv_cache
examining superblock
examining mapping array
examining hint array
examining discard bitset

$ sudo lvchange -an vg_ernie/lv_cache


With the same results:

$ sudo vgchange -ay
   device-mapper: reload ioctl on   (253:6) failed: Invalid argument
   0 logical volume(s) in volume group "vg_ernie" now active


A bit puzzling is that the status of the needs_check flag appears to be
"unknown":

$ sudo lvs -a -o +lv_check_needed
   LV                        VG          Attr          LSize    Pool
Origin                  Data%   Meta%   Move Log Cpy%Sync Convert CheckNeeded
   [lv_cache]            vg_ernie CRi-a-C--- 232.88g
unknown
   lv_system             vg_ernie Cwi---C---   <1.82t [lv_cache]
[lv_system_corig]
unknown
   [lv_system_corig] vg_ernie owi---C---   <1.82t
unknown


The live system I am running these commands from is a Fedora 33:

$ uname -a
Linux localhost-live 5.8.15-301.fc33.x86_64 #1 SMP Thu Oct 15 16:58:06 UTC
2020 x86_64 x86_64 x86_64 GNU/Linux

$ sudo lvm version
   LVM version:       2.03.10(2) (2020-08-09)
   Library version: 1.02.173 (2020-08-09)
   Driver version:   4.42.0
   Configuration:    ./configure --build=x86_64-redhat-linux-gnu --
host=x86_64-redhat-linux-gnu --program-prefix= --disable-dependency-tracking
--prefix=/usr --exec-prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin --
sysconfdir=/etc --datadir=/usr/share --includedir=/usr/include --libdir=/usr/
lib64 --libexecdir=/usr/libexec --localstatedir=/var --sharedstatedir=/var/lib
--mandir=/usr/share/man --infodir=/usr/share/info --with-default-dm-run-dir=/
run --with-default-run-dir=/run/lvm --with-default-pid-dir=/run --with-
default-locking-dir=/run/lock/lvm --with-usrlibdir=/usr/lib64 --enable-fsadm
--enable-write_install --with-user= --with-group= --with-device-uid=0 --with-
device-gid=6 --with-device-mode=0660 --enable-pkgconfig --enable-cmdlib --
enable-dmeventd --enable-blkid_wiping --with-cluster=internal --enable-
cmirrord --with-udevdir=/usr/lib/udev/rules.d --enable-udev_sync --with-
thin=internal --with-cache=internal --enable-lvmpolld --enable-lvmlockd-dlm --
enable-lvmlockd-dlmcontrol --enable-lvmlockd-sanlock --enable-dbus-service --
enable-notify-dbus --enable-dmfilemapd --with-writecache=internal --with-
vdo=internal --with-vdo-format=/usr/bin/vdoformat --disable-silent-rules


Is it possible that `cache_check --clear-needs-check-flag does not clear
needs_check flag` does not actually clear the needs_check flag in my case?


Any help to get the system back online (without data loss, if possible) is
appreciated!

Best regards,
Dennis
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