[Samba] io_uring cause data corruption

[Jeremy Allison]

On Sat, May 02, 2020 at 11:34:41AM +0200, A L wrote:
> ########
> I also tried various combinations of io_uring settings.
> 
> io_uring:sqpoll = true/false
> io_uring:num_entries = 2, 4, 8, 64, 128 (default), 256
> 
> Between each test i do "echo 3 > /proc/sys/vm/drop_caches" and restart the
> samba service.
> 
> One difference I noticed is that there is now only one [io_wqe_worker-0] io
> thread active when copying from this USB disk. This is probably because it
> is so slow, about 25MB/s maximum read speed. This seems to have an impact on
> where the corruptions happen in the files. All files have a corrupt/zeroed
> block at the end of the file, 99% of the time at the same place, as seen
> here https://paste.tnonline.net/files/Zdq7YKOfzogc_ext4_copy_io_uring.png
> 
> So, now I think we have at least ruled out Btrfs as filesystem as culprit
> with the io_uring.
> 
> You mentioned a wire trace of the SMB traffic. Can you provide some examples
> on how I do that?

Wireshark. Capture on TCP port 445.

> Perhaps I should open a bug on the Bugzilla tracker and continue this
> discussion there?

Thanks.