Re: [Bug Report]: generic/085 trigger a XFS panic on kernel 4.14-rc2

[Dave Chinner <david@fromorbit.com>]

On Sat, Sep 30, 2017 at 11:28:57AM +0800, Zorro Lang wrote:
> Hi,
> 
> I hit a panic[1] when I ran xfstests on debug kernel v4.14-rc2
> (with xfsprogs 4.13.1), and I can reproduce it on the same machine
> twice. But I can't reproduce it on another machine.
> 
> Maybe there're some hardware specific requirement to trigger this panic. I
> tested on normal disk partition, but the disk is multi stripes RAID device.
> I didn't get the mkfs output of g/085, bug I found the default mkfs output
> (mkfs.xfs -f /dev/sda3) is:
> 
> meta-data=/dev/sda3              isize=512    agcount=16, agsize=982528 blks
>          =                       sectsz=512   attr=2, projid32bit=1
>          =                       crc=1        finobt=1, sparse=0, rmapbt=0, reflink=0
> data     =                       bsize=1024   blocks=15720448, imaxpct=25
>          =                       sunit=512    swidth=1024 blks
> naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
> log      =internal log           bsize=1024   blocks=10240, version=2
>          =                       sectsz=512   sunit=32 blks, lazy-count=1
> realtime =none                   extsz=4096   blocks=0, rtextents=0

FWIW, I've come across a few of these log recovery crashes recently
when reworking mkfs.xfs. The cause of them has always been either a
log being too small or a mismatch between log size and log stripe
unit configuration. The typical sign of that was either a
negative buffer length like this one (XFS (dm-0): Invalid block
length (0xfffffed8) for buffer) or the head/tail block initially
being calculated before/after the actual log and so the log offset
was negative.

I'm guessing the recent log validity checking we've added isn't as
robust as it should be, but I haven't had time to dig into it yet.
I've debugged the issues far enough to point to mkfs being wrong
with xfs_logprint - it runs the same head/tail recovery code as the
kernel so typically crashes on the same problems as the kernel. It's
much easier to debug in userspace with gdb, though.....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com