Merge tag 'locking-core-2023-05-05' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull locking updates from Ingo Molnar:

 - Introduce local{,64}_try_cmpxchg() - a slightly more optimal
   primitive, which will be used in perf events ring-buffer code

 - Simplify/modify rwsems on PREEMPT_RT, to address writer starvation

 - Misc cleanups/fixes

* tag 'locking-core-2023-05-05' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  locking/atomic: Correct (cmp)xchg() instrumentation
  locking/x86: Define arch_try_cmpxchg_local()
  locking/arch: Wire up local_try_cmpxchg()
  locking/generic: Wire up local{,64}_try_cmpxchg()
  locking/atomic: Add generic try_cmpxchg{,64}_local() support
  locking/rwbase: Mitigate indefinite writer starvation
  locking/arch: Rename all internal __xchg() names to __arch_xchg()

2 files changed, 13 insertions, 2 deletions

diff --git a/arch/powerpc/include/asm/cmpxchg.h b/arch/powerpc/include/asm/cmpxchg.h
index d0ea0571e79a..dbb50c06f0bf 100644
--- a/arch/powerpc/include/asm/cmpxchg.h
+++ b/arch/powerpc/include/asm/cmpxchg.h
@@ -229,7 +229,7 @@ __xchg_local(void *ptr, unsigned long x, unsigned int size)
 		return __xchg_u64_local(ptr, x);
 #endif
 	}
-	BUILD_BUG_ON_MSG(1, "Unsupported size for __xchg");
+	BUILD_BUG_ON_MSG(1, "Unsupported size for __xchg_local");
 	return x;
 }
 
@@ -248,7 +248,7 @@ __xchg_relaxed(void *ptr, unsigned long x, unsigned int size)
 		return __xchg_u64_relaxed(ptr, x);
 #endif
 	}
-	BUILD_BUG_ON_MSG(1, "Unsupported size for __xchg_local");
+	BUILD_BUG_ON_MSG(1, "Unsupported size for __xchg_relaxed");
 	return x;
 }
 #define arch_xchg_local(ptr,x)						     \
diff --git a/arch/powerpc/include/asm/local.h b/arch/powerpc/include/asm/local.h
index bc4bd19b7fc2..45492fb5bf22 100644
--- a/arch/powerpc/include/asm/local.h
+++ b/arch/powerpc/include/asm/local.h
@@ -90,6 +90,17 @@ static __inline__ long local_cmpxchg(local_t *l, long o, long n)
 	return t;
 }
 
+static __inline__ bool local_try_cmpxchg(local_t *l, long *po, long n)
+{
+	long o = *po, r;
+
+	r = local_cmpxchg(l, o, n);
+	if (unlikely(r != o))
+		*po = r;
+
+	return likely(r == o);
+}
+
 static __inline__ long local_xchg(local_t *l, long n)
 {
 	long t;