On Wed, Feb 14, 2018 at 01:08:07PM -0500, Brian Foster wrote: > On Wed, Feb 14, 2018 at 08:49:12AM -0800, Darrick J. Wong wrote: > > On Wed, Feb 14, 2018 at 08:09:39AM -0500, Brian Foster wrote: > > > On Wed, Feb 14, 2018 at 09:02:20AM +1100, Dave Chinner wrote: > > > Yep. It's a specially crafted symlink creation on a small FSB, v4 > > > filesystem with fragmented free space. We log symlink buffers on v4 > > > filesystems without any header, so the buffer content is not dictated by > > > any internal fs metadata format. If the link target is large enough to > > > span multiple blocks and free space is fragmented such that those blocks > > > are discontiguous, we can end up logging (solely) the first byte of the > > > last buffer of the link target. I'd completely forgotten about that whacky corner case in the v4 format. :( > > > This is actually reproducible on demand so I'll just append a basic > > > recipe rather than collect the debug data and whatnot.. > > > > > > Brian > > > > > > --- 8< --- > > > > > > dev=<dev> > > > mnt=/mnt > > > > > > sym=`for i in $(seq 0 512); do echo -n a; done` > > > > > > mkfs.xfs -f -mcrc=0 -bsize=512 -dsize=25m $dev > > > mount $dev $mnt > > > > > > dd if=/dev/zero of=$mnt/spc1 > > > ~/xfstests-dev/src/punch-alternating $mnt/spc1 > > > dd if=/dev/zero of=$mnt/spc2 > > > xfs_io -c "fpunch 5m 25m" $mnt/spc2 > > > > > > for i in $(seq 0 2); do > > > ln -s $sym $mnt/link.$i > > > xfs_io -c fsync $mnt > > > done > > > > > > umount $mnt > > > > Did one of the "fragment free space, do stuff" xfstests hit this? If > > not, would it be worth turning into a test? > > > > This was just an experiment on this patch. I haven't run xfstests so I > can't say for sure whether some existing test would have caught it > (though I suspect Dave would have hit the problem by now, if so). I'm Nope, a v4 512 byte block size filesystem is so far outside my normal test config matrix it's not funny. In fact, I almost never test on v4 filesystems anymore, and I rarely think of them when developing new code as it's essentially a legacy format now.... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
