atomic: skip alignment check for try_cmpxchg() old arg

PATCH Applied Arnd Bergmann 3 participants 3 messages Oct 6, 2025 – Oct 21, 2025

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Arnd Bergmann

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2025-10-06 11:07 UTC #0 lore raw

PATCH 1/1 atomic: skip alignment check for try_cmpxchg() old arg

From: Arnd Bergmann <[email protected]>

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 <[email protected]>

Link https://lore.kernel.org/all/[email protected]/ open here

Signed-off-by Arnd Bergmann <[email protected]>

---
 include/linux/atomic/atomic-instrumented.h | 26 +++++++++++-----------
 scripts/atomic/gen-atomic-instrumented.sh  | 11 +++++----
 2 files changed, 20 insertions(+), 17 deletions(-)

include/linux/atomic/atomic-instrumented.h +13 ~~-13~~

index 9409a6ddf3e0..37ab6314a9f7 100644
@@ -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

scripts/atomic/gen-atomic-instrumented.sh +7 -4

index 592f3ec89b5f..9c1d53f81eb2 100755
@@ -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...)

Signature · 1 line

2.39.5

Finn Thain

Tested-by on v1 1/1

2025-10-08 06:24 UTC #1 lore raw

Quoted 12 lines · Arnd Bergmann

From: Arnd Bergmann <[email protected]>
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").

Quoted 6 lines

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 <[email protected]>

Tested-by Finn Thain <[email protected]>

Quoted 7 lines

Link https://lore.kernel.org/all/[email protected]/ open here
Signed-off-by Arnd Bergmann <[email protected]>
---
 include/linux/atomic/atomic-instrumented.h | 26 +++++++++++-----------
 scripts/atomic/gen-atomic-instrumented.sh  | 11 +++++----
 2 files changed, 20 insertions(+), 17 deletions(-)

tip-bot2 for Arnd Bergmann

merge bot Applied

2025-10-21 10:35 UTC #2 lore raw

[tip: locking/core] atomic: Skip alignment check for try_cmpxchg() old arg

In reply to Arnd Bergmann

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     44472d1b83127e579c798ff92a07ae86d98b61b9
Gitweb:        https://git.kernel.org/tip/44472d1b83127e579c798ff92a07ae86d98b61b9
Author:        Arnd Bergmann <[email protected]>
AuthorDate:    Mon, 06 Oct 2025 13:07:32 +02:00
Committer:     Peter Zijlstra <[email protected]>
CommitterDate: Tue, 21 Oct 2025 12:31:56 +02:00

atomic: Skip alignment check for try_cmpxchg() old arg

Reported-by Finn Thain <[email protected]>

Signed-off-by Arnd Bergmann <[email protected]>

Signed-off-by Peter Zijlstra (Intel) <[email protected]>

Link https://lore.kernel.org/all/[email protected]/ open here

---
 include/linux/atomic/atomic-instrumented.h | 26 ++++++++++-----------
 scripts/atomic/gen-atomic-instrumented.sh  | 11 +++++----
 2 files changed, 20 insertions(+), 17 deletions(-)

include/linux/atomic/atomic-instrumented.h +13 ~~-13~~

index 9409a6d..37ab631 100644
@@ -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

scripts/atomic/gen-atomic-instrumented.sh +7 -4

index 592f3ec..9c1d53f 100755
@@ -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...)