From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz@infradead.org>
Date: Mon, 25 Oct 2021 09:57:28 +0000
Subject: Re: [PATCH] locking: remove spin_lock_flags() etc
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To: Arnd Bergmann <arnd@kernel.org>
Cc: Waiman Long <longman@redhat.com>, Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>, Arnd Bergmann <arnd@arndb.de>, Boqun Feng <boqun.feng@gmail.com>, Jonas Bonn <jonas@southpole.se>, Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>, Stafford Horne <shorne@gmail.com>, "James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>, Helge Deller <deller@gmx.de>, Michael Ellerman <mpe@ellerman.id.au>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Paul Mackerras <paulus@samba.org>, Heiko Carstens <hca@linux.ibm.com>, Vasily Gorbik <gor@linux.ibm.com>, Christian Borntraeger <borntraeger@de.ibm.com>, Alexander Gordeev <agordeev@linux.ibm.com>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-ia64@vger.kernel.org, Openrisc <openrisc@lists.librecores.org>, Parisc List <linux-parisc@vger.kernel.org>, linuxppc-dev <linuxppc-dev@lists.ozlabs.org>, linux-s390 <linux-s390@vger.kernel.org>

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 :/