Re: context switch within RCU read-side critical section in next-20260518+ with PREEMPT_RT

[Mateusz Guzik]

On Thu, May 21, 2026 at 1:51 PM Bert Karwatzki <spasswolf@xxxxxx> wrote:
>
>
> >
> > Can you please do the following:
> > 1. go back to the known crashing-tag, add my fix, verify you still get
> > the amd splat and then try out the fix provided by Thomas
> > 2. regardless if the above helps, can you boot a kernel built with
> > CONFIG_KASAN=y
> >
> > fwiw I verified my patch works fine with KASAN, including by
> > intentionally miscalculating the size of the target buffer and seeing
> > a nice splat from it so I'm confident I'm not corrupting anything.
> > However, as there are new mallocs + free flying around at early boot,
> > it is *plausible* amd was getting zeroed memory without asking for it
> > and it worked by accident.
>
> I think the warnning from amdgpu is only displayed with CONFIG_LOCKDEP=y, so
> your "improved fix" does not silence the warning from amdgpu.
>
> The additional fix from Thomas fixes the amdgpu warning.
>

I just wanted to confirm my patch does not *cause* issues, at worst
uncovers them.

> I also built the kernel with CONFIG_KASAN and get no error messages.
>

nice

I presume Thomas will handle getting the amdgpu patch to the right
people, I think it will be fine to drop all the mailing lists and the
cc's. :-)

So overall I think we are done here.

Thank you for testing and sorry for the breakage.