Several architectures define arch_try_local_cmpxchg macro using
internal temporary variables named ___old, __old or _old. Remove
temporary varible in local_try_cmpxchg to avoid variable shadowing.
No functional change intended.
Fixes: d994f2c8e241 ("locking/arch: Wire up local_try_cmpxchg()")
Reported-by: Charlemagne Lasse <[email protected]>
Closes: https://lore.kernel.org/lkml/CAFGhKbyxtuk=LoW-E3yLXgcmR93m+Dfo5-u9oQA_YC5Fcy_t9g@mail.gmail.com/
Cc: Will Deacon <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Huacai Chen <[email protected]>
Cc: WANG Xuerui <[email protected]>
Cc: Jiaxun Yang <[email protected]>
Cc: Jun Yi <[email protected]>
Cc: Thomas Bogendoerfer <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Signed-off-by: Uros Bizjak <[email protected]>
---
arch/loongarch/include/asm/local.h | 4 ++--
arch/mips/include/asm/local.h | 4 ++--
arch/x86/include/asm/local.h | 4 ++--
3 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/arch/loongarch/include/asm/local.h b/arch/loongarch/include/asm/local.h
index 83e995b30e47..c49675852bdc 100644
--- a/arch/loongarch/include/asm/local.h
+++ b/arch/loongarch/include/asm/local.h
@@ -63,8 +63,8 @@ static inline long local_cmpxchg(local_t *l, long old, long new)
static inline bool local_try_cmpxchg(local_t *l, long *old, long new)
{
- typeof(l->a.counter) *__old = (typeof(l->a.counter) *) old;
- return try_cmpxchg_local(&l->a.counter, __old, new);
+ return try_cmpxchg_local(&l->a.counter,
+ (typeof(l->a.counter) *) old, new);
}
#define local_xchg(l, n) (atomic_long_xchg((&(l)->a), (n)))
diff --git a/arch/mips/include/asm/local.h b/arch/mips/include/asm/local.h
index 5daf6fe8e3e9..e6ae3df0349d 100644
--- a/arch/mips/include/asm/local.h
+++ b/arch/mips/include/asm/local.h
@@ -101,8 +101,8 @@ static __inline__ long local_cmpxchg(local_t *l, long old, long new)
static __inline__ bool local_try_cmpxchg(local_t *l, long *old, long new)
{
- typeof(l->a.counter) *__old = (typeof(l->a.counter) *) old;
- return try_cmpxchg_local(&l->a.counter, __old, new);
+ return try_cmpxchg_local(&l->a.counter,
+ (typeof(l->a.counter) *) old, new);
}
#define local_xchg(l, n) (atomic_long_xchg((&(l)->a), (n)))
diff --git a/arch/x86/include/asm/local.h b/arch/x86/include/asm/local.h
index 56d4ef604b91..635132a12778 100644
--- a/arch/x86/include/asm/local.h
+++ b/arch/x86/include/asm/local.h
@@ -127,8 +127,8 @@ static inline long local_cmpxchg(local_t *l, long old, long new)
static inline bool local_try_cmpxchg(local_t *l, long *old, long new)
{
- typeof(l->a.counter) *__old = (typeof(l->a.counter) *) old;
- return try_cmpxchg_local(&l->a.counter, __old, new);
+ return try_cmpxchg_local(&l->a.counter,
+ (typeof(l->a.counter) *) old, new);
}
/* Always has a lock prefix */
--
2.41.0
Use local_try_cmpxchg instead of local_cmpxchg (*ptr, old, new) == old
in __perf_output_begin. x86 CMPXCHG instruction returns success in ZF
flag, so this change saves a compare after cmpxchg (and related move
instruction in front of cmpxchg).
Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg
fails. There is no need to re-read the value in the loop.
No functional change intended.
Cc: Peter Zijlstra <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Ian Rogers <[email protected]>
Cc: Adrian Hunter <[email protected]>
Signed-off-by: Uros Bizjak <[email protected]>
---
kernel/events/ring_buffer.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index a0433f37b024..fb1e180b5f0a 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -191,9 +191,10 @@ __perf_output_begin(struct perf_output_handle *handle,
perf_output_get_handle(handle);
+ offset = local_read(&rb->head);
do {
+ head = offset;
tail = READ_ONCE(rb->user_page->data_tail);
- offset = head = local_read(&rb->head);
if (!rb->overwrite) {
if (unlikely(!ring_buffer_has_space(head, tail,
perf_data_size(rb),
@@ -217,7 +218,7 @@ __perf_output_begin(struct perf_output_handle *handle,
head += size;
else
head -= size;
- } while (local_cmpxchg(&rb->head, offset, head) != offset);
+ } while (!local_try_cmpxchg(&rb->head, &offset, head));
if (backward) {
offset = head;
--
2.41.0
The following commit has been merged into the perf/core branch of tip:
Commit-ID: 1af61adb3a23192023fec1733bd4c8500f53e546
Gitweb: https://git.kernel.org/tip/1af61adb3a23192023fec1733bd4c8500f53e546
Author: Uros Bizjak <[email protected]>
AuthorDate: Sat, 08 Jul 2023 11:00:37 +02:00
Committer: Peter Zijlstra <[email protected]>
CommitterDate: Mon, 10 Jul 2023 09:52:36 +02:00
perf/ring_buffer: Use local_try_cmpxchg in __perf_output_begin
Use local_try_cmpxchg instead of local_cmpxchg (*ptr, old, new) == old
in __perf_output_begin. x86 CMPXCHG instruction returns success in ZF
flag, so this change saves a compare after cmpxchg (and related move
instruction in front of cmpxchg).
Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg
fails. There is no need to re-read the value in the loop.
No functional change intended.
Signed-off-by: Uros Bizjak <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
---
kernel/events/ring_buffer.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index a0433f3..fb1e180 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -191,9 +191,10 @@ __perf_output_begin(struct perf_output_handle *handle,
perf_output_get_handle(handle);
+ offset = local_read(&rb->head);
do {
+ head = offset;
tail = READ_ONCE(rb->user_page->data_tail);
- offset = head = local_read(&rb->head);
if (!rb->overwrite) {
if (unlikely(!ring_buffer_has_space(head, tail,
perf_data_size(rb),
@@ -217,7 +218,7 @@ __perf_output_begin(struct perf_output_handle *handle,
head += size;
else
head -= size;
- } while (local_cmpxchg(&rb->head, offset, head) != offset);
+ } while (!local_try_cmpxchg(&rb->head, &offset, head));
if (backward) {
offset = head;
The following commit has been merged into the perf/core branch of tip:
Commit-ID: d6b45484c130f4095313ae3edeb4aae662c12fb1
Gitweb: https://git.kernel.org/tip/d6b45484c130f4095313ae3edeb4aae662c12fb1
Author: Uros Bizjak <[email protected]>
AuthorDate: Sat, 08 Jul 2023 11:00:36 +02:00
Committer: Peter Zijlstra <[email protected]>
CommitterDate: Mon, 10 Jul 2023 09:52:36 +02:00
locking/arch: Avoid variable shadowing in local_try_cmpxchg()
Several architectures define arch_try_local_cmpxchg macro using
internal temporary variables named ___old, __old or _old. Remove
temporary varible in local_try_cmpxchg to avoid variable shadowing.
No functional change intended.
Fixes: d994f2c8e241 ("locking/arch: Wire up local_try_cmpxchg()")
Closes: https://lore.kernel.org/lkml/CAFGhKbyxtuk=LoW-E3yLXgcmR93m+Dfo5-u9oQA_YC5Fcy_t9g@mail.gmail.com/
Reported-by: Charlemagne Lasse <[email protected]>
Signed-off-by: Uros Bizjak <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
---
arch/loongarch/include/asm/local.h | 4 ++--
arch/mips/include/asm/local.h | 4 ++--
arch/x86/include/asm/local.h | 4 ++--
3 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/arch/loongarch/include/asm/local.h b/arch/loongarch/include/asm/local.h
index 83e995b..c496758 100644
--- a/arch/loongarch/include/asm/local.h
+++ b/arch/loongarch/include/asm/local.h
@@ -63,8 +63,8 @@ static inline long local_cmpxchg(local_t *l, long old, long new)
static inline bool local_try_cmpxchg(local_t *l, long *old, long new)
{
- typeof(l->a.counter) *__old = (typeof(l->a.counter) *) old;
- return try_cmpxchg_local(&l->a.counter, __old, new);
+ return try_cmpxchg_local(&l->a.counter,
+ (typeof(l->a.counter) *) old, new);
}
#define local_xchg(l, n) (atomic_long_xchg((&(l)->a), (n)))
diff --git a/arch/mips/include/asm/local.h b/arch/mips/include/asm/local.h
index 5daf6fe..e6ae3df 100644
--- a/arch/mips/include/asm/local.h
+++ b/arch/mips/include/asm/local.h
@@ -101,8 +101,8 @@ static __inline__ long local_cmpxchg(local_t *l, long old, long new)
static __inline__ bool local_try_cmpxchg(local_t *l, long *old, long new)
{
- typeof(l->a.counter) *__old = (typeof(l->a.counter) *) old;
- return try_cmpxchg_local(&l->a.counter, __old, new);
+ return try_cmpxchg_local(&l->a.counter,
+ (typeof(l->a.counter) *) old, new);
}
#define local_xchg(l, n) (atomic_long_xchg((&(l)->a), (n)))
diff --git a/arch/x86/include/asm/local.h b/arch/x86/include/asm/local.h
index 56d4ef6..635132a 100644
--- a/arch/x86/include/asm/local.h
+++ b/arch/x86/include/asm/local.h
@@ -127,8 +127,8 @@ static inline long local_cmpxchg(local_t *l, long old, long new)
static inline bool local_try_cmpxchg(local_t *l, long *old, long new)
{
- typeof(l->a.counter) *__old = (typeof(l->a.counter) *) old;
- return try_cmpxchg_local(&l->a.counter, __old, new);
+ return try_cmpxchg_local(&l->a.counter,
+ (typeof(l->a.counter) *) old, new);
}
/* Always has a lock prefix */