[PATCH] locking/qspinlock: Always evaluate lockevent* non-event parameter once

[PATCH] locking/qspinlock: Always evaluate lockevent* non-event parameter once

[Waiman Long]

The inc parameter of lockevent_add() and the cond parameter of
lockevent_cond_inc() are only evaluated when CONFIG_LOCK_EVENT_COUNTS
is on. That can cause problem if those parameters are expressions
with side effect like a "++". Fix this by evaluating those non-event
parameters once even if CONFIG_LOCK_EVENT_COUNTS is off. This will also
eliminate the need of the __maybe_unused attribute to the wait_early
local variable in pv_wait_node().

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Waiman Long <longman@redhat.com>
---
 kernel/locking/lock_events.h        | 4 ++--
 kernel/locking/qspinlock_paravirt.h | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/locking/lock_events.h b/kernel/locking/lock_events.h
index a6016b91803d..d2345e9c0190 100644
--- a/kernel/locking/lock_events.h
+++ b/kernel/locking/lock_events.h
@@ -53,8 +53,8 @@ static inline void __lockevent_add(enum lock_events event, int inc)
 #else  /* CONFIG_LOCK_EVENT_COUNTS */
 
 #define lockevent_inc(ev)
-#define lockevent_add(ev, c)
-#define lockevent_cond_inc(ev, c)
+#define lockevent_add(ev, c)		do { (void)(c); } while (0)
+#define lockevent_cond_inc(ev, c)	do { (void)(c); } while (0)
 
 #endif /* CONFIG_LOCK_EVENT_COUNTS */
 
diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
index ae2b12f68b90..169950fe1aad 100644
--- a/kernel/locking/qspinlock_paravirt.h
+++ b/kernel/locking/qspinlock_paravirt.h
@@ -294,7 +294,7 @@ static void pv_wait_node(struct mcs_spinlock *node, struct mcs_spinlock *prev)
 {
 	struct pv_node *pn = (struct pv_node *)node;
 	struct pv_node *pp = (struct pv_node *)prev;
-	bool __maybe_unused wait_early;
+	bool wait_early;
 	int loop;
 
 	for (;;) {
-- 
2.39.3

Re: [PATCH] locking/qspinlock: Always evaluate lockevent* non-event parameter once

[Boqun Feng]

On Mon, Mar 18, 2024 at 08:50:04PM -0400, Waiman Long wrote:
> The inc parameter of lockevent_add() and the cond parameter of
> lockevent_cond_inc() are only evaluated when CONFIG_LOCK_EVENT_COUNTS
> is on. That can cause problem if those parameters are expressions
> with side effect like a "++". Fix this by evaluating those non-event
> parameters once even if CONFIG_LOCK_EVENT_COUNTS is off. This will also
> eliminate the need of the __maybe_unused attribute to the wait_early
> local variable in pv_wait_node().
> 
> Suggested-by: Ingo Molnar <mingo@kernel.org>
> Signed-off-by: Waiman Long <longman@redhat.com>

Reviewed-by: Boqun Feng <boqun.feng@gmail.com>

Regards,
Boqun

> ---
>  kernel/locking/lock_events.h        | 4 ++--
>  kernel/locking/qspinlock_paravirt.h | 2 +-
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/locking/lock_events.h b/kernel/locking/lock_events.h
> index a6016b91803d..d2345e9c0190 100644
> --- a/kernel/locking/lock_events.h
> +++ b/kernel/locking/lock_events.h
> @@ -53,8 +53,8 @@ static inline void __lockevent_add(enum lock_events event, int inc)
>  #else  /* CONFIG_LOCK_EVENT_COUNTS */
>  
>  #define lockevent_inc(ev)
> -#define lockevent_add(ev, c)
> -#define lockevent_cond_inc(ev, c)
> +#define lockevent_add(ev, c)		do { (void)(c); } while (0)
> +#define lockevent_cond_inc(ev, c)	do { (void)(c); } while (0)
>  
>  #endif /* CONFIG_LOCK_EVENT_COUNTS */
>  
> diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
> index ae2b12f68b90..169950fe1aad 100644
> --- a/kernel/locking/qspinlock_paravirt.h
> +++ b/kernel/locking/qspinlock_paravirt.h
> @@ -294,7 +294,7 @@ static void pv_wait_node(struct mcs_spinlock *node, struct mcs_spinlock *prev)
>  {
>  	struct pv_node *pn = (struct pv_node *)node;
>  	struct pv_node *pp = (struct pv_node *)prev;
> -	bool __maybe_unused wait_early;
> +	bool wait_early;
>  	int loop;
>  
>  	for (;;) {
> -- 
> 2.39.3
> 

[tip: locking/core] locking/qspinlock: Always evaluate lockevent* non-event parameter once

[tip-bot2 for Waiman Long]

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

Commit-ID:     3774b28d8f3b9e8a946beb9550bee85e5454fc9f
Gitweb:        https://git.kernel.org/tip/3774b28d8f3b9e8a946beb9550bee85e5454fc9f
Author:        Waiman Long <longman@redhat.com>
AuthorDate:    Mon, 18 Mar 2024 20:50:04 -04:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Thu, 21 Mar 2024 20:45:17 +01:00

locking/qspinlock: Always evaluate lockevent* non-event parameter once

The 'inc' parameter of lockevent_add() and the cond parameter of
lockevent_cond_inc() are only evaluated when CONFIG_LOCK_EVENT_COUNTS
is on. That can cause problem if those parameters are expressions
with side effect like a "++". Fix this by evaluating those non-event
parameters once even if CONFIG_LOCK_EVENT_COUNTS is off. This will also
eliminate the need of the __maybe_unused attribute to the wait_early
local variable in pv_wait_node().

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/20240319005004.1692705-1-longman@redhat.com
---
 kernel/locking/lock_events.h        | 4 ++--
 kernel/locking/qspinlock_paravirt.h | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/locking/lock_events.h b/kernel/locking/lock_events.h
index a6016b9..d2345e9 100644
--- a/kernel/locking/lock_events.h
+++ b/kernel/locking/lock_events.h
@@ -53,8 +53,8 @@ static inline void __lockevent_add(enum lock_events event, int inc)
 #else  /* CONFIG_LOCK_EVENT_COUNTS */
 
 #define lockevent_inc(ev)
-#define lockevent_add(ev, c)
-#define lockevent_cond_inc(ev, c)
+#define lockevent_add(ev, c)		do { (void)(c); } while (0)
+#define lockevent_cond_inc(ev, c)	do { (void)(c); } while (0)
 
 #endif /* CONFIG_LOCK_EVENT_COUNTS */
 
diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
index ae2b12f..169950f 100644
--- a/kernel/locking/qspinlock_paravirt.h
+++ b/kernel/locking/qspinlock_paravirt.h
@@ -294,7 +294,7 @@ static void pv_wait_node(struct mcs_spinlock *node, struct mcs_spinlock *prev)
 {
 	struct pv_node *pn = (struct pv_node *)node;
 	struct pv_node *pp = (struct pv_node *)prev;
-	bool __maybe_unused wait_early;
+	bool wait_early;
 	int loop;
 
 	for (;;) {