Re: [PATCH] locking: remove spin_lock_flags() etc

Peter Zijlstra
2021-10-25T09:57:28Z

On Sat, Oct 23, 2021 at 06:04:57PM +0200, Arnd Bergmann wrote:
> On Sat, Oct 23, 2021 at 3:37 AM Waiman Long <longman@redhat.com> wrote:
> >> On 10/22/21 7:59 AM, Arnd Bergmann wrote:
> > > From: Arnd Bergmann <arnd@arndb.de>
> > >
> > > As this is all dead code, just remove it and the helper functions built
> > > around it. For arch/ia64, the inline asm could be cleaned up, but
> > > it seems safer to leave it untouched.
> > >
> > > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> >
> > Does that mean we can also remove the GENERIC_LOCKBREAK config option
> > from the Kconfig files as well?
>
> I couldn't figure this out.
>
> What I see is that the only architectures setting GENERIC_LOCKBREAK are
> nds32, parisc, powerpc, s390, sh and sparc64, while the only architectures
> implementing arch_spin_is_contended() are arm32, csky and ia64.
>
> The part I don't understand is whether the option actually does anything
> useful any more after commit d89c70356acf ("locking/core: Remove break_lock
> field when CONFIG_GENERIC_LOCKBREAK=y").

Urgh, what a mess.. AFAICT there's still code in
kernel/locking/spinlock.c that relies on it. Specifically when
GENERIC_LOCKBREAK=y we seem to create _lock*() variants that are
basically TaS locks which drop preempt/irq disable while spinning.

Anybody having this on and not having native TaS locks is in for a rude
surprise I suppose... sparc64 being the obvious candidate there :/