[dm-devel] fuzzing bcachefs with dm-flakey

[Mikulas Patocka]

On Mon, 29 May 2023, Matthew Wilcox wrote:

> On Mon, May 29, 2023 at 04:59:40PM -0400, Mikulas Patocka wrote:
> > Hi
> > 
> > I improved the dm-flakey device mapper target, so that it can do random 
> > corruption of read and write bios - I uploaded it here: 
> > https://people.redhat.com/~mpatocka/testcases/bcachefs/dm-flakey.c
> > 
> > I set up dm-flakey, so that it corrupts 10% of read bios and 10% of write 
> > bios with this command:
> > dmsetup create flakey --table "0 `blockdev --getsize /dev/ram0` flakey /dev/ram0 0 0 1 4 random_write_corrupt 100000000 random_read_corrupt 100000000"
> 
> I'm not suggesting that any of the bugs you've found are invalid, but 10%
> seems really high.  Is it reasonable to expect any filesystem to cope
> with that level of broken hardware?  Can any of our existing ones cope
> with that level of flakiness?  I mean, I've got some pretty shoddy USB
> cables, but ...

If you reduce the corruption probability, it will take more iterations to 
hit the bugs.

So, for the "edit-compile-test" loop, the probability should be as high as 
possible, just to save the developer's time on testing.

Mikulas