Alpha has native LL/SC instructions (LDL_L/STL_C, LDQ_L/STQ_C) that
provide atomic read-modify-write capability, and already selects
ARCH_HAVE_NMI_SAFE_CMPXCHG.

Selecting ARCH_SUPPORTS_ATOMIC_RMW enables MUTEX_SPIN_ON_OWNER and
RWSEM_SPIN_ON_OWNER on SMP, allowing optimistic spinning on contended
locks rather than immediately sleeping.

Assisted-by: Claude:claude-opus-4-6
Signed-off-by: Matt Turner <mattst88@gmail.com>
---
 arch/alpha/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git ./arch/alpha/Kconfig ./arch/alpha/Kconfig
index 4329743757e3..57c91ed67b71 100644
--- ./arch/alpha/Kconfig
+++ ./arch/alpha/Kconfig
@@ -10,6 +10,7 @@ config ALPHA
 	select ARCH_MODULE_NEEDS_WEAK_PER_CPU if SMP
 	select ARCH_NO_PREEMPT
 	select ARCH_NO_SG_CHAIN
+	select ARCH_SUPPORTS_ATOMIC_RMW
 	select ARCH_SUPPORTS_PAGE_TABLE_CHECK
 	select ARCH_USE_CMPXCHG_LOCKREF
 	select FORCE_PCI
-- 
2.52.0