Data Corruption bug with Samba's vfs_iouring and Linux 5.6.7/5.7rc3

[Jeremy Allison]

On Thu, May 07, 2020 at 12:35:42PM -0600, Jens Axboe wrote:
> On 5/7/20 12:31 PM, Jeremy Allison wrote:
> > 
> > Look at how quickly someone spotted disk corruption
> > because of the change in userspace-visible behavior
> > of the io_uring interface. We only shipped that code
> > 03 March 2020 and someone *already* found it.
> 
> I _think_ that will only happen on regular files if you use RWF_NOWAIT
> or similar, for regular blocking it should not happen. So I don't think
> you're at risk there, though I do think that anyone should write
> applications with short IOs in mind or they will run into surprises down
> the line. Should have been more clear!

Well we definitely considered short IOs writing the
server code, but as the protocol allows that to be
visible to the clients (in fact it has explicit
fields meant to deal with it) it wasn't considered
vital to hide them from clients.

We'll certainly fix up short reads for the iouring
module, but it's less clear we should mess with
our existing blocking threaded pread/pwrite code
to deal with them. Possibly goes into the bucket
of "belt and braces, couldn't possibly hurt" :-).

Thanks for the clarification !