Re: [PATCH v9 0/3] mm/gup: disallow GUP writing to file-backed mappings by default

On Sun, May 14, 2023 at 10:14:46PM -0700, Christoph Hellwig wrote:

On Sun, May 14, 2023 at 08:20:04PM +0100, Lorenzo Stoakes wrote:

quoted

As discussed at LSF/MM, on the flight over I wrote a little repro [0] which
reliably triggers the ext4 warning by recreating the scenario described
above, using a small userland program and kernel module.

This code is not perfect (plane code :) but does seem to do the job
adequately, also obviously this should only be run in a VM environment
where data loss is acceptable (in my case a small qemu instance).

It would be really awesome if you could wire it up with and submit it
to xfstests.

Sure am happy to take a look at that! Also happy if David finds it useful in any
way for this unit tests.

The kernel module interface is a bit sketchy (it takes a user address which it
blindly pins for you) so it's not something that should be run in any unsafe
environment but as long as we are ok with that :)