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From:   Uros Bizjak <ubizjak@gmail.com>
To:     linux-kernel@vger.kernel.org, x86@kernel.org,
        xen-devel@lists.xenproject.org
Cc:     Uros Bizjak <ubizjak@gmail.com>, Will Deacon <will@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        Mark Rutland <mark.rutland@arm.com>
Subject: [PATCH v2 1/3] locking/generic: Add generic support for sync_try_cmpxchg and its fallback
Date:   Sun,  1 Oct 2023 12:39:09 +0200
Message-ID: <20231001104053.9644-1-ubizjak@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Provide the generic sync_try_cmpxchg function from the
raw_ prefixed version, also adding explicit instrumentation.

The patch amends existing scripts to generate sync_try_cmpxchg
locking primitive and its raw_sync_try_cmpxchg fallback, while
leaving existing macros from try_cmpxchg family unchanged.

The target can define its own arch_sync_try_cmpxchg to override the
generic version of raw_sync_try_cmpxchg. This allows the target
to generate more optimal assembly than the generic version.

Additionally, the patch renames two scripts to better reflect
whet they really do.

Cc: Will Deacon <will@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
---
v2: Improve commit description.
---
 include/linux/atomic/atomic-arch-fallback.h | 15 +++++++++-
 include/linux/atomic/atomic-instrumented.h  | 10 ++++++-
 scripts/atomic/gen-atomic-fallback.sh       | 33 +++++++++++----------
 scripts/atomic/gen-atomic-instrumented.sh   |  3 +-
 4 files changed, 43 insertions(+), 18 deletions(-)

diff --git a/include/linux/atomic/atomic-arch-fallback.h b/include/linux/atomic/atomic-arch-fallback.h
index b83ef19da13d..5e95faa959c4 100644
--- a/include/linux/atomic/atomic-arch-fallback.h
+++ b/include/linux/atomic/atomic-arch-fallback.h
@@ -428,6 +428,19 @@ extern void raw_cmpxchg128_relaxed_not_implemented(void);
 
 #define raw_sync_cmpxchg arch_sync_cmpxchg
 
+#ifdef arch_sync_try_cmpxchg
+#define raw_sync_try_cmpxchg arch_sync_try_cmpxchg
+#else
+#define raw_sync_try_cmpxchg(_ptr, _oldp, _new) \
+({ \
+	typeof(*(_ptr)) *___op = (_oldp), ___o = *___op, ___r; \
+	___r = raw_sync_cmpxchg((_ptr), ___o, (_new)); \
+	if (unlikely(___r != ___o)) \
+		*___op = ___r; \
+	likely(___r == ___o); \
+})
+#endif
+
 /**
  * raw_atomic_read() - atomic load with relaxed ordering
  * @v: pointer to atomic_t
@@ -4649,4 +4662,4 @@ raw_atomic64_dec_if_positive(atomic64_t *v)
 }
 
 #endif /* _LINUX_ATOMIC_FALLBACK_H */
-// 2fdd6702823fa842f9cea57a002e6e4476ae780c
+// eec048affea735b8464f58e6d96992101f8f85f1
diff --git a/include/linux/atomic/atomic-instrumented.h b/include/linux/atomic/atomic-instrumented.h
index d401b406ef7c..54d7bbe0aeaa 100644
--- a/include/linux/atomic/atomic-instrumented.h
+++ b/include/linux/atomic/atomic-instrumented.h
@@ -4998,6 +4998,14 @@ atomic_long_dec_if_positive(atomic_long_t *v)
 	raw_try_cmpxchg128_local(__ai_ptr, __ai_oldp, __VA_ARGS__); \
 })
 
+#define sync_try_cmpxchg(ptr, ...) \
+({ \
+	typeof(ptr) __ai_ptr = (ptr); \
+	kcsan_mb(); \
+	instrument_atomic_read_write(__ai_ptr, sizeof(*__ai_ptr)); \
+	raw_sync_try_cmpxchg(__ai_ptr, __VA_ARGS__); \
+})
+
 
 #endif /* _LINUX_ATOMIC_INSTRUMENTED_H */
-// 1568f875fef72097413caab8339120c065a39aa4
+// 2cc4bc990fef44d3836ec108f11b610f3f438184
diff --git a/scripts/atomic/gen-atomic-fallback.sh b/scripts/atomic/gen-atomic-fallback.sh
index a45154cefa48..f80d69cfeb1f 100755
--- a/scripts/atomic/gen-atomic-fallback.sh
+++ b/scripts/atomic/gen-atomic-fallback.sh
@@ -223,14 +223,15 @@ gen_xchg_fallbacks()
 
 gen_try_cmpxchg_fallback()
 {
+	local prefix="$1"; shift
 	local cmpxchg="$1"; shift;
-	local order="$1"; shift;
+	local suffix="$1"; shift;
 
 cat <<EOF
-#define raw_try_${cmpxchg}${order}(_ptr, _oldp, _new) \\
+#define raw_${prefix}try_${cmpxchg}${suffix}(_ptr, _oldp, _new) \\
 ({ \\
 	typeof(*(_ptr)) *___op = (_oldp), ___o = *___op, ___r; \\
-	___r = raw_${cmpxchg}${order}((_ptr), ___o, (_new)); \\
+	___r = raw_${prefix}${cmpxchg}${suffix}((_ptr), ___o, (_new)); \\
 	if (unlikely(___r != ___o)) \\
 		*___op = ___r; \\
 	likely(___r == ___o); \\
@@ -259,11 +260,11 @@ gen_try_cmpxchg_order_fallback()
 	fi
 
 	printf "#else\n"
-	gen_try_cmpxchg_fallback "${cmpxchg}" "${order}"
+	gen_try_cmpxchg_fallback "" "${cmpxchg}" "${order}"
 	printf "#endif\n\n"
 }
 
-gen_try_cmpxchg_fallbacks()
+gen_try_cmpxchg_order_fallbacks()
 {
 	local cmpxchg="$1"; shift;
 
@@ -272,15 +273,17 @@ gen_try_cmpxchg_fallbacks()
 	done
 }
 
-gen_cmpxchg_local_fallbacks()
+gen_def_and_try_cmpxchg_fallback()
 {
+	local prefix="$1"; shift
 	local cmpxchg="$1"; shift
+	local suffix="$1"; shift
 
-	printf "#define raw_${cmpxchg} arch_${cmpxchg}\n\n"
-	printf "#ifdef arch_try_${cmpxchg}\n"
-	printf "#define raw_try_${cmpxchg} arch_try_${cmpxchg}\n"
+	printf "#define raw_${prefix}${cmpxchg}${suffix} arch_${prefix}${cmpxchg}${suffix}\n\n"
+	printf "#ifdef arch_${prefix}try_${cmpxchg}${suffix}\n"
+	printf "#define raw_${prefix}try_${cmpxchg}${suffix} arch_${prefix}try_${cmpxchg}${suffix}\n"
 	printf "#else\n"
-	gen_try_cmpxchg_fallback "${cmpxchg}" ""
+	gen_try_cmpxchg_fallback "${prefix}" "${cmpxchg}" "${suffix}"
 	printf "#endif\n\n"
 }
 
@@ -302,15 +305,15 @@ for xchg in "xchg" "cmpxchg" "cmpxchg64" "cmpxchg128"; do
 done
 
 for cmpxchg in "cmpxchg" "cmpxchg64" "cmpxchg128"; do
-	gen_try_cmpxchg_fallbacks "${cmpxchg}"
+	gen_try_cmpxchg_order_fallbacks "${cmpxchg}"
 done
 
-for cmpxchg in "cmpxchg_local" "cmpxchg64_local" "cmpxchg128_local"; do
-	gen_cmpxchg_local_fallbacks "${cmpxchg}" ""
+for cmpxchg in "cmpxchg" "cmpxchg64" "cmpxchg128"; do
+	gen_def_and_try_cmpxchg_fallback "" "${cmpxchg}" "_local"
 done
 
-for cmpxchg in "sync_cmpxchg"; do
-	printf "#define raw_${cmpxchg} arch_${cmpxchg}\n\n"
+for cmpxchg in "cmpxchg"; do
+	gen_def_and_try_cmpxchg_fallback "sync_" "${cmpxchg}" ""
 done
 
 grep '^[a-z]' "$1" | while read name meta args; do
diff --git a/scripts/atomic/gen-atomic-instrumented.sh b/scripts/atomic/gen-atomic-instrumented.sh
index 8f8f8e3b20f9..592f3ec89b5f 100755
--- a/scripts/atomic/gen-atomic-instrumented.sh
+++ b/scripts/atomic/gen-atomic-instrumented.sh
@@ -169,7 +169,8 @@ for xchg in "xchg" "cmpxchg" "cmpxchg64" "cmpxchg128" "try_cmpxchg" "try_cmpxchg
 	done
 done
 
-for xchg in "cmpxchg_local" "cmpxchg64_local" "cmpxchg128_local" "sync_cmpxchg" "try_cmpxchg_local" "try_cmpxchg64_local" "try_cmpxchg128_local"; do
+for xchg in "cmpxchg_local" "cmpxchg64_local" "cmpxchg128_local" "sync_cmpxchg" \
+	    "try_cmpxchg_local" "try_cmpxchg64_local" "try_cmpxchg128_local" "sync_try_cmpxchg"; do
 	gen_xchg "${xchg}" ""
 	printf "\n"
 done
-- 
2.41.0