linux-kernel - Re: [PATCH/RFC] locking/spinlocks: Make __raw

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Date: Sat, 2 Mar 2024 23:25:51 -0500
From: Waiman Long <longman@...hat.com>
To: Geert Uytterhoeven <geert+renesas@...der.be>,
 Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Will Deacon <will@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
 Arnd Bergmann <arnd@...db.de>
Cc: linux-sh@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH/RFC] locking/spinlocks: Make __raw_* lock ops static

On 3/1/24 15:43, Geert Uytterhoeven wrote:
> sh/sdk7786_defconfig (CONFIG_GENERIC_LOCKBREAK=y and
> CONFIG_DEBUG_LOCK_ALLOC=n):
>
> kernel/locking/spinlock.c:68:17: warning: no previous prototype for '__raw_spin_lock' [-Wmissing-prototypes]
> kernel/locking/spinlock.c:80:26: warning: no previous prototype for '__raw_spin_lock_irqsave' [-Wmissing-prototypes]
> kernel/locking/spinlock.c:98:17: warning: no previous prototype for '__raw_spin_lock_irq' [-Wmissing-prototypes]
> kernel/locking/spinlock.c:103:17: warning: no previous prototype for '__raw_spin_lock_bh' [-Wmissing-prototypes]
> kernel/locking/spinlock.c:68:17: warning: no previous prototype for '__raw_read_lock' [-Wmissing-prototypes]
> kernel/locking/spinlock.c:80:26: warning: no previous prototype for '__raw_read_lock_irqsave' [-Wmissing-prototypes]
> kernel/locking/spinlock.c:98:17: warning: no previous prototype for '__raw_read_lock_irq' [-Wmissing-prototypes]
> kernel/locking/spinlock.c:103:17: warning: no previous prototype for '__raw_read_lock_bh' [-Wmissing-prototypes]
> kernel/locking/spinlock.c:68:17: warning: no previous prototype for '__raw_write_lock' [-Wmissing-prototypes]
> kernel/locking/spinlock.c:80:26: warning: no previous prototype for '__raw_write_lock_irqsave' [-Wmissing-prototypes]
> kernel/locking/spinlock.c:98:17: warning: no previous prototype for '__raw_write_lock_irq' [-Wmissing-prototypes]
> kernel/locking/spinlock.c:103:17: warning: no previous prototype for '__raw_write_lock_bh' [-Wmissing-prototypes]
>
> Fix this by making the __raw_* lock ops static.
>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> ---
> Compile-tested only.
>
> Is SH really the only SMP platform where CONFIG_GENERIC_LOCKBREAK=y?
> ---
>   kernel/locking/spinlock.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/locking/spinlock.c b/kernel/locking/spinlock.c
> index 8475a0794f8c5ad2..7009b568e6255d64 100644
> --- a/kernel/locking/spinlock.c
> +++ b/kernel/locking/spinlock.c
> @@ -65,7 +65,7 @@ EXPORT_PER_CPU_SYMBOL(__mmiowb_state);
>    * towards that other CPU that it should break the lock ASAP.
>    */
>   #define BUILD_LOCK_OPS(op, locktype)					\
> -void __lockfunc __raw_##op##_lock(locktype##_t *lock)			\
> +static void __lockfunc __raw_##op##_lock(locktype##_t *lock)		\
>   {									\
>   	for (;;) {							\
>   		preempt_disable();					\
> @@ -77,7 +77,7 @@ void __lockfunc __raw_##op##_lock(locktype##_t *lock)			\
>   	}								\
>   }									\
>   									\
> -unsigned long __lockfunc __raw_##op##_lock_irqsave(locktype##_t *lock)	\
> +static unsigned long __lockfunc __raw_##op##_lock_irqsave(locktype##_t *lock) \
>   {									\
>   	unsigned long flags;						\
>   									\
> @@ -95,12 +95,12 @@ unsigned long __lockfunc __raw_##op##_lock_irqsave(locktype##_t *lock)	\
>   	return flags;							\
>   }									\
>   									\
> -void __lockfunc __raw_##op##_lock_irq(locktype##_t *lock)		\
> +static void __lockfunc __raw_##op##_lock_irq(locktype##_t *lock)	\
>   {									\
>   	_raw_##op##_lock_irqsave(lock);					\
>   }									\
>   									\
> -void __lockfunc __raw_##op##_lock_bh(locktype##_t *lock)		\
> +static void __lockfunc __raw_##op##_lock_bh(locktype##_t *lock)		\
>   {									\
>   	unsigned long flags;						\
>   									\

This may not work if CONFIG_GENERIC_LOCKBREAK is defined. We had been 
talking about taking out CONFIG_GENERIC_LOCKBREAK before. See the thread 
in [1]. However, we didn't proceed further at that time as we weren't 
totally sure if there were still some configurations that required 
CONFIG_GENERIC_LOCKBREAK.

[1] https://lore.kernel.org/lkml/20211022120058.1031690-1-arnd@kernel.org/

Anyway, without taking out CONFIG_GENERIC_LOCKBREAK, the proper way to 
fix this issue is probably to declare the proper function prototypes in 
include/linux/rwlock_api_smp.h and include/linux/spinlock_api_smp.h when 
CONFIG_GENERIC_LOCKBREAK is defined.

Cheers,
Longman