On Sat, Oct 23, 2021 at 06:04:57PM +0200, Arnd Bergmann wrote:

On Sat, Oct 23, 2021 at 3:37 AM Waiman Long [off-list ref] wrote:

quoted

quoted

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 :/