Re: linux-next regression: SNP Guest boot hangs with certain cpu/mem config combination

[Kirill A. Shutemov]

On Thu, Mar 27, 2025 at 11:02:24AM -0400, Steven Rostedt wrote:
> On Thu, 27 Mar 2025 16:43:43 +0200
> "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
> 
> > > > The only option I see so far is to drop static branch from this path.
> > > > 
> > > > But I am not sure if it the only case were we use static branch from CPU
> > > > hotplug callbacks.
> > > > 
> > > > Any other ideas?  
> > > 
> > > 
> > > Hmmm, didn't take too close a look here, but there is the
> > > static_key_slow_dec_cpuslocked() variant, would that work here? Is the issue
> > > the caller may or may not have the cpu_hotplug lock?  
> > 
> > Yes. This is generic page alloc path and it can be called with and without
> > the lock.
> 
> Note, it's not the static_branch that is an issue, it's enabling/disabling
> the static branch that is. Changing a static branch takes a bit of work as
> it does modify the kernel text.
> 
> Is it possible to delay the update via a workqueue?

Ah. Good point. Should work. I'll give it try.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov