diff mbox series

[-next] arm64/spinlock: fix a -Wunused-function warning

Message ID 20200123162945.7705-1-cai@lca.pw (mailing list archive)
State New, archived
Headers show
Series [-next] arm64/spinlock: fix a -Wunused-function warning | expand

Commit Message

Qian Cai Jan. 23, 2020, 4:29 p.m. UTC
The commit f5bfdc8e3947 ("locking/osq: Use optimized spinning loop for
arm64") introduced a warning from Clang because vcpu_is_preempted() is
compiled away,

kernel/locking/osq_lock.c:25:19: warning: unused function 'node_cpu'
[-Wunused-function]
static inline int node_cpu(struct optimistic_spin_node *node)
                  ^
1 warning generated.

Since vcpu_is_preempted() had already been defined in
include/linux/sched.h as false, just comment out the redundant macro, so
it can still be served for the documentation purpose.

Fixes: f5bfdc8e3947 ("locking/osq: Use optimized spinning loop for arm64")
Signed-off-by: Qian Cai <cai@lca.pw>
---
 arch/arm64/include/asm/spinlock.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Comments

Will Deacon Jan. 23, 2020, 4:56 p.m. UTC | #1
On Thu, Jan 23, 2020 at 11:29:45AM -0500, Qian Cai wrote:
> The commit f5bfdc8e3947 ("locking/osq: Use optimized spinning loop for
> arm64") introduced a warning from Clang because vcpu_is_preempted() is
> compiled away,
> 
> kernel/locking/osq_lock.c:25:19: warning: unused function 'node_cpu'
> [-Wunused-function]
> static inline int node_cpu(struct optimistic_spin_node *node)
>                   ^
> 1 warning generated.
> 
> Since vcpu_is_preempted() had already been defined in
> include/linux/sched.h as false, just comment out the redundant macro, so
> it can still be served for the documentation purpose.
> 
> Fixes: f5bfdc8e3947 ("locking/osq: Use optimized spinning loop for arm64")
> Signed-off-by: Qian Cai <cai@lca.pw>
> ---
>  arch/arm64/include/asm/spinlock.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h
> index 102404dc1e13..b05f82e8ba19 100644
> --- a/arch/arm64/include/asm/spinlock.h
> +++ b/arch/arm64/include/asm/spinlock.h
> @@ -17,7 +17,8 @@
>   *
>   * See:
>   * https://lore.kernel.org/lkml/20200110100612.GC2827@hirez.programming.kicks-ass.net
> + *
> + * #define vcpu_is_preempted(cpu)	false
>   */
> -#define vcpu_is_preempted(cpu)	false

Damn, the whole point of this was to warn in the case that
vcpu_is_preempted() does get defined for arm64. Can we force it to evaluate
the macro argument instead (e.g. ({ (cpu), false; }) or something)?

Will
Waiman Long Jan. 23, 2020, 5:11 p.m. UTC | #2
On 1/23/20 11:29 AM, Qian Cai wrote:
> The commit f5bfdc8e3947 ("locking/osq: Use optimized spinning loop for
> arm64") introduced a warning from Clang because vcpu_is_preempted() is
> compiled away,
>
> kernel/locking/osq_lock.c:25:19: warning: unused function 'node_cpu'
> [-Wunused-function]
> static inline int node_cpu(struct optimistic_spin_node *node)
>                   ^
> 1 warning generated.
>
> Since vcpu_is_preempted() had already been defined in
> include/linux/sched.h as false, just comment out the redundant macro, so
> it can still be served for the documentation purpose.
>
> Fixes: f5bfdc8e3947 ("locking/osq: Use optimized spinning loop for arm64")
> Signed-off-by: Qian Cai <cai@lca.pw>
> ---
>  arch/arm64/include/asm/spinlock.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h
> index 102404dc1e13..b05f82e8ba19 100644
> --- a/arch/arm64/include/asm/spinlock.h
> +++ b/arch/arm64/include/asm/spinlock.h
> @@ -17,7 +17,8 @@
>   *
>   * See:
>   * https://lore.kernel.org/lkml/20200110100612.GC2827@hirez.programming.kicks-ass.net
> + *
> + * #define vcpu_is_preempted(cpu)	false
>   */
> -#define vcpu_is_preempted(cpu)	false
>  
>  #endif /* __ASM_SPINLOCK_H */

Does adding a __maybe_unused tag help to prevent the warning? Like

diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c
index 6ef600aa0f47..0722655af34f 100644
--- a/kernel/locking/osq_lock.c
+++ b/kernel/locking/osq_lock.c
@@ -22,7 +22,7 @@ static inline int encode_cpu(int cpu_nr)
        return cpu_nr + 1;
 }
 
-static inline int node_cpu(struct optimistic_spin_node *node)
+static inline int __maybe_unused node_cpu(struct optimistic_spin_node
*node)
 {
        return node->cpu - 1;
 }

Cheers,
Longman
Qian Cai Jan. 23, 2020, 5:23 p.m. UTC | #3
> On Jan 23, 2020, at 11:56 AM, Will Deacon <will@kernel.org> wrote:
> 
> Damn, the whole point of this was to warn in the case that
> vcpu_is_preempted() does get defined for arm64. Can we force it to evaluate
> the macro argument instead (e.g. ({ (cpu), false; }) or something)?

That should work. Let me test it out and rinse.
Qian Cai Jan. 23, 2020, 5:31 p.m. UTC | #4
> On Jan 23, 2020, at 11:56 AM, Will Deacon <will@kernel.org> wrote:
> 
> Damn, the whole point of this was to warn in the case that
> vcpu_is_preempted() does get defined for arm64. Can we force it to evaluate
> the macro argument instead (e.g. ({ (cpu), false; }) or something)?

Actually, static inline should be better.

#define vcpu_is_preempted vcpu_is_preempted
static inline bool vcpu_is_preempted(int cpu)
{
	return false;
}
Waiman Long Jan. 23, 2020, 5:36 p.m. UTC | #5
On 1/23/20 12:31 PM, Qian Cai wrote:
>
>> On Jan 23, 2020, at 11:56 AM, Will Deacon <will@kernel.org> wrote:
>>
>> Damn, the whole point of this was to warn in the case that
>> vcpu_is_preempted() does get defined for arm64. Can we force it to evaluate
>> the macro argument instead (e.g. ({ (cpu), false; }) or something)?
> Actually, static inline should be better.
>
> #define vcpu_is_preempted vcpu_is_preempted
> static inline bool vcpu_is_preempted(int cpu)
> {
> 	return false;
> }
>
Yes, that may work.

Cheers,
Longman
diff mbox series

Patch

diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h
index 102404dc1e13..b05f82e8ba19 100644
--- a/arch/arm64/include/asm/spinlock.h
+++ b/arch/arm64/include/asm/spinlock.h
@@ -17,7 +17,8 @@ 
  *
  * See:
  * https://lore.kernel.org/lkml/20200110100612.GC2827@hirez.programming.kicks-ass.net
+ *
+ * #define vcpu_is_preempted(cpu)	false
  */
-#define vcpu_is_preempted(cpu)	false
 
 #endif /* __ASM_SPINLOCK_H */