Re: [PATCHv2] efi/unaccepted: Fix soft lockups caused by parallel memory acceptance

[Ard Biesheuvel]

On Tue, 17 Oct 2023 at 11:44, Kirill A. Shutemov
<kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
>
> On Tue, Oct 17, 2023 at 09:42:13AM +0200, Ard Biesheuvel wrote:
> > On Mon, 16 Oct 2023 at 23:39, Kirill A. Shutemov
> > <kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
> > >
> > > On Mon, Oct 16, 2023 at 06:55:41PM +0100, Matthew Wilcox wrote:
> > > > On Mon, Oct 16, 2023 at 07:31:22PM +0300, Kirill A. Shutemov wrote:
> > > > >   v2:
> > > > >    - Fix deadlock (Vlastimil);
> > > > >    - Fix comments (Vlastimil);
> > > > >    - s/cond_resched()/cpu_relax()/ -- cond_resched() cannot be called
> > > > >      from atomic context;
> > > >
> > > > Isn't there an implicit cpu_relax() while we're spinning?  Does this
> > > > really accomplish anything?
> > >
> > > You are right. It is useless. I will drop it in v3.
> > >
> >
> > I can drop that bit when applying the patch.
> >
> > One question I have is whether the sequence
> >
> > spin_lock_irqsave(&unaccepted_memory_lock, flags);
> > ...
> > spin_unlock(&unaccepted_memory_lock);
> > arch_accept_memory(phys_start, phys_end);
> > spin_lock(&unaccepted_memory_lock);
> > ...
> > spin_unlock_irqrestore(&unaccepted_memory_lock, flags);
> >
> > is considered sound and is supported by all architectures?
>
> I am not an locking expert and only tested it on x86. But what potential
> issue do you see?
>

Not sure. It just looks slightly out of place, and I am curious
whether all architectures tolerate this asymmetric use.