Re: fstest/btrfs/220 tigger a check-integrity warning

[Wang Yugui <wangyugui@e16-tech.com>]

Hi,

> > xfstest/btrfs/220 tigger check-integrity warning.
> >
> > btrfs source:  5.15.0-0.rc5 with btrfs pull for rc6
> >
> > btrfs kernel config:
> > CONFIG_BTRFS_FS=m
> > CONFIG_BTRFS_FS_POSIX_ACL=y
> > CONFIG_BTRFS_FS_CHECK_INTEGRITY=y
> > # CONFIG_BTRFS_FS_RUN_SANITY_TESTS is not set
> > # CONFIG_BTRFS_DEBUG is not set
> > CONFIG_BTRFS_ASSERT=y
> > CONFIG_BTRFS_FS_REF_VERIFY=y
> >
> > reproduce frequency: 100%
> >
> > [ 1917.552758] btrfs: attempt to write superblock which
> > references block M
> > @5242880 (sdb2/5242880/0) which is not flushed out of disk's
> > write cache (block
> > flush_gen=1, dev->flush_gen=0)!
> >
> Anything special about /dev/sdb? I can reproduce if test device is zram
> since zram seems to handle FUA in its way.
> For normal device backing by file/disk, the test always passed on my side.

Thanks for this info.  

I checked it on some disks.
passed:
	SSD/SAS	PX05SMQ040
failed:
	SSD/SAS		HUSMH842
	SSD/NVMe	SM963/SM1715

I noticed that PX05SMQ040 is 'WCE:1/write back', but HUSMH842 is'WCE:0/write
through', both SM963 and SM1715 are 
' [0:0] : 0     Volatile Write Cache Not Present/write through'

I failed to test it on zram.
#mkfs.btrfs /dev/zram0
btrfs-progs v5.10.1
See http://btrfs.wiki.kernel.org for more information.

Detected a SSD, turning off metadata duplication.  Mkfs with -m dup if you want to force metadata duplication.
ERROR: '/dev/zram0' is too small to make a usable filesystem
ERROR: minimum size for each btrfs device is 47185920

Best Regards
Wang Yugui (wangyugui@e16-tech.com)
2021/10/22