asm-generic/atomic: Add try_cmpxchg() fallbacks

Only x86 provides try_cmpxchg() outside of the atomic_t interfaces,
provide generic fallbacks to create this interface from the widely
available cmpxchg() function.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/159870621515.1229682.15506193091065001742.stgit@devnote2

scripts/atomic/gen-atomic-fallback.sh

@@ -144,15 +144,11 @@ gen_proto_order_variants()
 	printf "#endif /* ${basename}_relaxed */\n\n"
 }
 
-gen_xchg_fallbacks()
+gen_order_fallbacks()
 {
 	local xchg="$1"; shift
+
 cat <<EOF
-#ifndef ${xchg}_relaxed
-#define ${xchg}_relaxed		${xchg}
-#define ${xchg}_acquire		${xchg}
-#define ${xchg}_release		${xchg}
-#else /* ${xchg}_relaxed */
 
 #ifndef ${xchg}_acquire
 #define ${xchg}_acquire(...) \\
@@ -169,11 +165,62 @@ cat <<EOF
 	__atomic_op_fence(${xchg}, __VA_ARGS__)
 #endif
 
-#endif /* ${xchg}_relaxed */
+EOF
+}
+
+gen_xchg_fallbacks()
+{
+	local xchg="$1"; shift
+	printf "#ifndef ${xchg}_relaxed\n"
+
+	gen_basic_fallbacks ${xchg}
+
+	printf "#else /* ${xchg}_relaxed */\n"
+
+	gen_order_fallbacks ${xchg}
+
+	printf "#endif /* ${xchg}_relaxed */\n\n"
+}
+
+gen_try_cmpxchg_fallback()
+{
+	local order="$1"; shift;
+
+cat <<EOF
+#ifndef ${ARCH}try_cmpxchg${order}
+#define ${ARCH}try_cmpxchg${order}(_ptr, _oldp, _new) \\
+({ \\
+	typeof(*(_ptr)) *___op = (_oldp), ___o = *___op, ___r; \\
+	___r = ${ARCH}cmpxchg${order}((_ptr), ___o, (_new)); \\
+	if (unlikely(___r != ___o)) \\
+		*___op = ___r; \\
+	likely(___r == ___o); \\
+})
+#endif /* ${ARCH}try_cmpxchg${order} */
 
 EOF
 }
 
+gen_try_cmpxchg_fallbacks()
+{
+	printf "#ifndef ${ARCH}try_cmpxchg_relaxed\n"
+	printf "#ifdef ${ARCH}try_cmpxchg\n"
+
+	gen_basic_fallbacks "${ARCH}try_cmpxchg"
+
+	printf "#endif /* ${ARCH}try_cmpxchg */\n\n"
+
+	for order in "" "_acquire" "_release" "_relaxed"; do
+		gen_try_cmpxchg_fallback "${order}"
+	done
+
+	printf "#else /* ${ARCH}try_cmpxchg_relaxed */\n"
+
+	gen_order_fallbacks "${ARCH}try_cmpxchg"
+
+	printf "#endif /* ${ARCH}try_cmpxchg_relaxed */\n\n"
+}
+
 cat << EOF
 // SPDX-License-Identifier: GPL-2.0
 
@@ -191,6 +238,8 @@ for xchg in "${ARCH}xchg" "${ARCH}cmpxchg" "${ARCH}cmpxchg64"; do
 	gen_xchg_fallbacks "${xchg}"
 done
 
+gen_try_cmpxchg_fallbacks
+
 grep '^[a-z]' "$1" | while read name meta args; do
 	gen_proto "${meta}" "${name}" "${ARCH}" "atomic" "int" ${args}
 done

scripts/atomic/gen-atomic-instrumented.sh

@@ -103,14 +103,31 @@ gen_xchg()
 	local xchg="$1"; shift
 	local mult="$1"; shift
 
+	if [ "${xchg%${xchg#try_cmpxchg}}" = "try_cmpxchg" ] ; then
+
 cat <<EOF
-#define ${xchg}(ptr, ...)						\\
-({									\\
-	typeof(ptr) __ai_ptr = (ptr);					\\
-	instrument_atomic_write(__ai_ptr, ${mult}sizeof(*__ai_ptr));		\\
-	arch_${xchg}(__ai_ptr, __VA_ARGS__);				\\
+#define ${xchg}(ptr, oldp, ...) \\
+({ \\
+	typeof(ptr) __ai_ptr = (ptr); \\
+	typeof(oldp) __ai_oldp = (oldp); \\
+	instrument_atomic_write(__ai_ptr, ${mult}sizeof(*__ai_ptr)); \\
+	instrument_atomic_write(__ai_oldp, ${mult}sizeof(*__ai_oldp)); \\
+	arch_${xchg}(__ai_ptr, __ai_oldp, __VA_ARGS__); \\
 })
 EOF
+
+	else
+
+cat <<EOF
+#define ${xchg}(ptr, ...) \\
+({ \\
+	typeof(ptr) __ai_ptr = (ptr); \\
+	instrument_atomic_write(__ai_ptr, ${mult}sizeof(*__ai_ptr)); \\
+	arch_${xchg}(__ai_ptr, __VA_ARGS__); \\
+})
+EOF
+
+	fi
 }
 
 gen_optional_xchg()
@@ -160,7 +177,7 @@ grep '^[a-z]' "$1" | while read name meta args; do
 	gen_proto "${meta}" "${name}" "atomic64" "s64" ${args}
 done
 
-for xchg in "xchg" "cmpxchg" "cmpxchg64"; do
+for xchg in "xchg" "cmpxchg" "cmpxchg64" "try_cmpxchg"; do
 	for order in "" "_acquire" "_release" "_relaxed"; do
 		gen_optional_xchg "${xchg}" "${order}"
 	done