Re: make misbehavior on ext2 in dax mode (was: a crash when running strace from persistent memory)

[Mikulas Patocka]

On Fri, 4 Sep 2020, Mikulas Patocka wrote:

> Hmm, so I've found another bug in dax mode.
> 
> If you extract the Linux kernel tree on dax-based ext2 filesystem (use the 
> real ext2 driver, not ext4), and then you run make twice, the second 
> invocation will rebuild everything. It seems like a problem with 
> timestamps.
> 
> mount -t ext2 -o dax /dev/pmem0 /mnt/ext2/
> cd /mnt/ext2/usr/src/git/linux-2.6
> make clean
> make -j12
> make -j12	<--- this rebuilds the whole tree, althought it shouldn't
> 
> I wasn't able to bisect it because this bug seems to be present in every 
> kernel I tried (back to 4.16.0). Ext4 doesn't seem to have this bug.
> 
> Mikulas

I've found out the root cause for this bug (XFS has it too) and I'm 
sending patches.

Mikulas