Re: read corruption with qemu master io_uring engine / linux master / btrfs(?)

[Nikolay Borisov <nborisov@suse.com>]

On 28.06.22 г. 12:08 ч., Dominique MARTINET wrote:
> I don't have any good reproducer so it's a bit difficult to specify,
> let's start with what I have...
> 
> I've got this one VM which has various segfaults all over the place when
> starting it with aio=io_uring for its disk as follow:
> 
>    qemu-system-x86_64 -drive file=qemu/atde-test,if=none,id=hd0,format=raw,cache=none,aio=io_uring \
>        -device virtio-blk-pci,drive=hd0 -m 8G -smp 4 -serial mon:stdio -enable-kvm

So cache=none means O_DIRECT and using io_uring. This really sounds 
similar to:

ca93e44bfb5fd7996b76f0f544999171f647f93b

This commit got merged into v5.17 so you shouldn't be seeing it on 5.17 
and onwards.

<snip>

> 
> Perhaps at this point it might be simpler to just try to take qemu out
> of the equation and issue many parallel reads to different offsets
> (overlapping?) of a large file in a similar way qemu io_uring engine
> does and check their contents?

Care to run the sample program in the aforementioned commit and verify 
it's not failing

> 
> 
> Thanks, and I'll probably follow up a bit tomorrow even if no-one has
> any idea, but even ideas of where to look would be appreciated.