Re: [PATCH] io_thread/x86: don't reset 'cs', 'ss', 'ds' and 'es' registers for io_threads

[Linus Torvalds <torvalds@linux-foundation.org>]

On Tue, May 11, 2021 at 9:24 PM Olivier Langlois <olivier@trillion01.com> wrote:
>
> I have reported an issue that I have with a user process using io_uring
> where when it core dumps, the dump fails to be generated.
> https://github.com/axboe/liburing/issues/346

I suspect most kernel developers don't have github notifications
enabled. I know I have them disabled because it would be *way* too
noisy not to.

But maybe Jens does for that libiouring part.

> Pavel did comment to my report and he did point out this thread as
> possibly a related issue.

I don't think this is related. The gdb confusion wouldn't affect core
dump generation.

I don't see why a core-dump shouldn't work from an IO thread these
days - the signal struct and synchronization should all be the same as
for a regular user thread.

That said, I do wonder if we should avoid generating core dumps from
the IO worker thread itself. The IO thread itself should never get a
SIGSEGV/SIGBUS anyway, it should have been turned into -EFAULT.

So maybe the

                if (current->flags & PF_IO_WORKER)
                        goto out;

in kernel/signal.c should be moved up above the do_coredump() logic regardless.

Jens, have you played with core-dumping when there are active io_uring
threads? There's a test-program in that github issue report..

              Linus