linux-kernel - [PATCH] atomic: skip alignment check for try

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Message-Id: <20251006110740.468309-1-arnd@kernel.org>
Date: Mon,  6 Oct 2025 13:07:32 +0200
From: Arnd Bergmann <arnd@...nel.org>
To: Will Deacon <will@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Boqun Feng <boqun.feng@...il.com>
Cc: Geert Uytterhoeven <geert@...ux-m68k.org>,
	Linux-Arch <linux-arch@...r.kernel.org>,
	linux-m68k@...r.kernel.org,
	Arnd Bergmann <arnd@...db.de>,
	Finn Thain <fthain@...ux-m68k.org>,
	Mark Rutland <mark.rutland@....com>,
	Gary Guo <gary@...yguo.net>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] atomic: skip alignment check for try_cmpxchg() old arg

From: Arnd Bergmann <arnd@...db.de>

The 'old' argument in atomic_try_cmpxchg() and related functions is a
pointer to a normal non-atomic integer number, which does not require
to be naturally aligned, unlike the atomic_t/atomic64_t types themselves.

In order to add an alignment check with CONFIG_DEBUG_ATOMIC into the
normal instrument_atomic_read_write() helper, change this check to use
the non-atomic instrument_read_write(), the same way that was done
earlier for try_cmpxchg() in commit ec570320b09f ("locking/atomic:
Correct (cmp)xchg() instrumentation").

This prevents warnings on m68k calling the 32-bit atomic_try_cmpxchg()
with 16-bit aligned arguments as well as several more architectures
including x86-32 when calling atomic64_try_cmpxchg() with 32-bit
aligned u64 arguments.

Reported-by: Finn Thain <fthain@...ux-m68k.org>
Link: https://lore.kernel.org/all/cover.1757810729.git.fthain@linux-m68k.org/
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 include/linux/atomic/atomic-instrumented.h | 26 +++++++++++-----------
 scripts/atomic/gen-atomic-instrumented.sh  | 11 +++++----
 2 files changed, 20 insertions(+), 17 deletions(-)

diff --git a/include/linux/atomic/atomic-instrumented.h b/include/linux/atomic/atomic-instrumented.h
index 9409a6ddf3e0..37ab6314a9f7 100644
--- a/include/linux/atomic/atomic-instrumented.h
+++ b/include/linux/atomic/atomic-instrumented.h
@@ -1276,7 +1276,7 @@ atomic_try_cmpxchg(atomic_t *v, int *old, int new)
 {
 	kcsan_mb();
 	instrument_atomic_read_write(v, sizeof(*v));
-	instrument_atomic_read_write(old, sizeof(*old));
+	instrument_read_write(old, sizeof(*old));
 	return raw_atomic_try_cmpxchg(v, old, new);
 }
 
@@ -1298,7 +1298,7 @@ static __always_inline bool
 atomic_try_cmpxchg_acquire(atomic_t *v, int *old, int new)
 {
 	instrument_atomic_read_write(v, sizeof(*v));
-	instrument_atomic_read_write(old, sizeof(*old));
+	instrument_read_write(old, sizeof(*old));
 	return raw_atomic_try_cmpxchg_acquire(v, old, new);
 }
 
@@ -1321,7 +1321,7 @@ atomic_try_cmpxchg_release(atomic_t *v, int *old, int new)
 {
 	kcsan_release();
 	instrument_atomic_read_write(v, sizeof(*v));
-	instrument_atomic_read_write(old, sizeof(*old));
+	instrument_read_write(old, sizeof(*old));
 	return raw_atomic_try_cmpxchg_release(v, old, new);
 }
 
@@ -1343,7 +1343,7 @@ static __always_inline bool
 atomic_try_cmpxchg_relaxed(atomic_t *v, int *old, int new)
 {
 	instrument_atomic_read_write(v, sizeof(*v));
-	instrument_atomic_read_write(old, sizeof(*old));
+	instrument_read_write(old, sizeof(*old));
 	return raw_atomic_try_cmpxchg_relaxed(v, old, new);
 }
 
@@ -2854,7 +2854,7 @@ atomic64_try_cmpxchg(atomic64_t *v, s64 *old, s64 new)
 {
 	kcsan_mb();
 	instrument_atomic_read_write(v, sizeof(*v));
-	instrument_atomic_read_write(old, sizeof(*old));
+	instrument_read_write(old, sizeof(*old));
 	return raw_atomic64_try_cmpxchg(v, old, new);
 }
 
@@ -2876,7 +2876,7 @@ static __always_inline bool
 atomic64_try_cmpxchg_acquire(atomic64_t *v, s64 *old, s64 new)
 {
 	instrument_atomic_read_write(v, sizeof(*v));
-	instrument_atomic_read_write(old, sizeof(*old));
+	instrument_read_write(old, sizeof(*old));
 	return raw_atomic64_try_cmpxchg_acquire(v, old, new);
 }
 
@@ -2899,7 +2899,7 @@ atomic64_try_cmpxchg_release(atomic64_t *v, s64 *old, s64 new)
 {
 	kcsan_release();
 	instrument_atomic_read_write(v, sizeof(*v));
-	instrument_atomic_read_write(old, sizeof(*old));
+	instrument_read_write(old, sizeof(*old));
 	return raw_atomic64_try_cmpxchg_release(v, old, new);
 }
 
@@ -2921,7 +2921,7 @@ static __always_inline bool
 atomic64_try_cmpxchg_relaxed(atomic64_t *v, s64 *old, s64 new)
 {
 	instrument_atomic_read_write(v, sizeof(*v));
-	instrument_atomic_read_write(old, sizeof(*old));
+	instrument_read_write(old, sizeof(*old));
 	return raw_atomic64_try_cmpxchg_relaxed(v, old, new);
 }
 
@@ -4432,7 +4432,7 @@ atomic_long_try_cmpxchg(atomic_long_t *v, long *old, long new)
 {
 	kcsan_mb();
 	instrument_atomic_read_write(v, sizeof(*v));
-	instrument_atomic_read_write(old, sizeof(*old));
+	instrument_read_write(old, sizeof(*old));
 	return raw_atomic_long_try_cmpxchg(v, old, new);
 }
 
@@ -4454,7 +4454,7 @@ static __always_inline bool
 atomic_long_try_cmpxchg_acquire(atomic_long_t *v, long *old, long new)
 {
 	instrument_atomic_read_write(v, sizeof(*v));
-	instrument_atomic_read_write(old, sizeof(*old));
+	instrument_read_write(old, sizeof(*old));
 	return raw_atomic_long_try_cmpxchg_acquire(v, old, new);
 }
 
@@ -4477,7 +4477,7 @@ atomic_long_try_cmpxchg_release(atomic_long_t *v, long *old, long new)
 {
 	kcsan_release();
 	instrument_atomic_read_write(v, sizeof(*v));
-	instrument_atomic_read_write(old, sizeof(*old));
+	instrument_read_write(old, sizeof(*old));
 	return raw_atomic_long_try_cmpxchg_release(v, old, new);
 }
 
@@ -4499,7 +4499,7 @@ static __always_inline bool
 atomic_long_try_cmpxchg_relaxed(atomic_long_t *v, long *old, long new)
 {
 	instrument_atomic_read_write(v, sizeof(*v));
-	instrument_atomic_read_write(old, sizeof(*old));
+	instrument_read_write(old, sizeof(*old));
 	return raw_atomic_long_try_cmpxchg_relaxed(v, old, new);
 }
 
@@ -5050,4 +5050,4 @@ atomic_long_dec_if_positive(atomic_long_t *v)
 
 
 #endif /* _LINUX_ATOMIC_INSTRUMENTED_H */
-// 8829b337928e9508259079d32581775ececd415b
+// f618ac667f868941a84ce0ab2242f1786e049ed4
diff --git a/scripts/atomic/gen-atomic-instrumented.sh b/scripts/atomic/gen-atomic-instrumented.sh
index 592f3ec89b5f..9c1d53f81eb2 100755
--- a/scripts/atomic/gen-atomic-instrumented.sh
+++ b/scripts/atomic/gen-atomic-instrumented.sh
@@ -12,7 +12,7 @@ gen_param_check()
 	local arg="$1"; shift
 	local type="${arg%%:*}"
 	local name="$(gen_param_name "${arg}")"
-	local rw="write"
+	local rw="atomic_write"
 
 	case "${type#c}" in
 	i) return;;
@@ -20,14 +20,17 @@ gen_param_check()
 
 	if [ ${type#c} != ${type} ]; then
 		# We don't write to constant parameters.
-		rw="read"
+		rw="atomic_read"
+	elif [ "${type}" = "p" ] ; then
+		# The "old" argument in try_cmpxchg() gets accessed non-atomically
+		rw="read_write"
 	elif [ "${meta}" != "s" ]; then
 		# An atomic RMW: if this parameter is not a constant, and this atomic is
 		# not just a 's'tore, this parameter is both read from and written to.
-		rw="read_write"
+		rw="atomic_read_write"
 	fi
 
-	printf "\tinstrument_atomic_${rw}(${name}, sizeof(*${name}));\n"
+	printf "\tinstrument_${rw}(${name}, sizeof(*${name}));\n"
 }
 
 #gen_params_checks(meta, arg...)
-- 
2.39.5