ramdisk problems in 4.0-rc1? (was Re: [PATCH 1/4] xfs/104: log size too small for 4k sector drives)

[Dave Chinner <david@fromorbit.com>]

[cc linux-fsdevel, Boaz and others]

On Wed, Feb 25, 2015 at 11:11:51AM -0500, Brian Foster wrote:
> On Wed, Feb 25, 2015 at 09:54:36AM +1100, Dave Chinner wrote:
> > From: Dave Chinner <dchinner@redhat.com>
> > 
> > xfs/104, xfs/119, xfs/291 and xfs/297 have small fixed log sizes. A
> > recent change to the kernel ramdisk changed it's physical sector
> > size from 512B to 4kB, and this results in mkfs calculating a log
> > size larger than the fixed test size and hence the tests fail.
> > 
> > Change the log size to a larger size that works with 4k sectors, and
> > also increase the size of the filesystem being created so that the
> > amount of data space in the filesystem does not change and hence
> > does not perturb the rest of the test.
> > 
> > Signed-off-by: Dave Chinner <dchinner@redhat.com>
> > ---
> 
> Well for some reason I can't mount a ramdisk on the current tot to test
> this. In fact, I can't mount _anything_ after the ramdisk mount attempt.
> The mount actually reports success too, but there's nothing there... :/
> 
> # modprobe brd
> # mkfs.xfs -f /dev/ram0 
> meta-data=/dev/ram0              isize=256    agcount=1, agsize=4096
> blks
>          =                       sectsz=4096  attr=2, projid32bit=1
>          =                       crc=0        finobt=0
> data     =                       bsize=4096   blocks=4096, imaxpct=25
>          =                       sunit=0      swidth=0 blks
> naming   =version 2              bsize=4096   ascii-ci=0 ftype=0
> log      =internal log           bsize=4096   blocks=1605, version=2
>          =                       sectsz=4096  sunit=1 blks, lazy-count=1
> realtime =none                   extsz=4096   blocks=0, rtextents=0
> # mount /dev/ram0 /mnt/
> # mount | grep mnt
> # umount  /mnt/
> umount: /mnt/: not mounted
> 
> ... and then I can't even mount my normal scratch device until after a
> reboot:
> 
> # mount /dev/test/scratch /mnt/
> # mount | grep mnt
> # umount  /mnt/
> umount: /mnt/: not mounted

Ok, so that's just plain broken. What's in dmesg?

As it is, I'm seeing plenty of weirdness in 4.0-rc1 on ramdisks as
well. Apart from the change to 4k physical sector size causing all
sorts of chaos with xfstests results due to it changing mkfs.xfs
behaviour, I'm also seeing this happen randomly:

....
Feb 25 11:48:35 test4 dave: run xfstest generic/083
Feb 25 11:48:37 test4 kernel: [ 8732.316223] XFS (ram1): Mounting V5 Filesystem
Feb 25 11:48:37 test4 kernel: [ 8732.318904] XFS (ram1): Ending clean mount
Feb 25 11:48:40 test4 kernel: [ 8735.871968] XFS (ram1): Unmounting Filesystem
Feb 25 11:48:40 test4 kernel: [ 8735.930160]  ram1: [POWERTEC] p1 p2 p3 p4 p5 p6 p7
Feb 25 11:48:40 test4 kernel: [ 8735.932081] ram1: p2 start 3158599292 is beyond EOD, truncated
Feb 25 11:48:40 test4 kernel: [ 8735.933983] ram1: p3 size 1627389952 extends beyond EOD, truncated
Feb 25 11:48:40 test4 kernel: [ 8735.936177] ram1: p4 size 1158021120 extends beyond EOD, truncated
Feb 25 11:48:40 test4 kernel: [ 8735.938269] ram1: p5 start 50924556 is beyond EOD, truncated
Feb 25 11:48:40 test4 kernel: [ 8735.940103] ram1: p6 size 67108864 extends beyond EOD, truncated
Feb 25 11:48:40 test4 kernel: [ 8735.942101] ram1: p7 start 4294967295 is beyond EOD, truncated
Feb 25 11:48:40 test4 dave: run xfstest generic/088
....

Something is causing partition rescans on ram devices that don't
have partitions, and this is new behaviour. Boaz, your commit
937af5ecd05 ("brd: Fix all partitions BUGs") seems the likely cause
of this problem I'm seeing - looks likea behaviour regression to
me as no other block device I have on any machine running the
same kernel throws these strange warnings from partition probing...

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com