Re: [PATCH] 9p/virtio: restrict page pinning to user_backed_iter() iovec

asmadeus
2025-12-18T23:15:25Z

Christian Schoenebeck wrote on Thu, Dec 18, 2025 at 04:14:45PM +0100:
> > Won't be the first time I can't reproduce, but what kind of workload are
> > you testing?
> > Anything that might help me try to reproduce (like VM cpu count/memory)
> > will be appreciated, corruptions are Bad...
>
> Debian Trixie guest running as 9p rootfs in QEMU, 4 cores, 16 GB.
>
> Compiling a bunch of projects with GCC works fine without errors, but with
> clang it's very simple for me to reproduce. E.g. just a very short C++ file
> that pulls in some system headers:
>
> #include <utility>
> #include <sys/cdefs.h>
> #include <limits>
>
> Then running 3 times: clang++ -c foo.cpp -std=c++17
>
> The first 2 clang runs succeed, the 3rd clang run then always blows up for
> anything else than cache=none, various spurious clang errors on those system
> headers like

Thanks, I can't reproduce with this example, but building linux with
`make LLVM=1` does blow up on debian... even with cache=none actually?

I couldn't reproduce running the same rootfs directory in a container so
I don't think I corrupted my image, it appears to be reading junk? short
reads perhaps?...
(Interestingly, it doesn't seem to blow up on an alpine rootfs, I wonder
what's different...)

I'm now getting late for work but at least there's something I can
reproduce, I'll have a closer look ASAP, thank you.

--
Dominique Martinet | Asmadeus