diff mbox series

[v3,1/5] arch,locking/atomic: arc: arch_cmpxchg should check data size

Message ID 20231121142347.241356-2-wuqiang.matt@bytedance.com
State New
Headers show
Series arch,locking/atomic: add arch_cmpxchg[64]_local | expand

Commit Message

wuqiang.matt Nov. 21, 2023, 2:23 p.m. UTC 
arch_cmpxchg() should check data size rather than pointer size in case
CONFIG_ARC_HAS_LLSC is defined. So rename __cmpxchg to __cmpxchg_32 to
emphasize it's explicit support of 32bit data size with BUILD_BUG_ON()
added to avoid any possible misuses with unsupported data types.

In case CONFIG_ARC_HAS_LLSC is undefined, arch_cmpxchg() uses spinlock
to accomplish SMP-safety, so the BUILD_BUG_ON checking is uncecessary.

v2 -> v3:
  - Patches regrouped and has the improvement for xtensa included
  - Comments refined to address why these changes are needed

v1 -> v2:
  - Try using native cmpxchg variants if avaialble, as Arnd advised

Signed-off-by: wuqiang.matt <wuqiang.matt@bytedance.com>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 arch/arc/include/asm/cmpxchg.h | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

Comments

Andi Shyti Nov. 22, 2023, 10:17 p.m. UTC | #1 
Hi Wuqiang,

On Tue, Nov 21, 2023 at 10:23:43PM +0800, wuqiang.matt wrote:
> arch_cmpxchg() should check data size rather than pointer size in case
> CONFIG_ARC_HAS_LLSC is defined. So rename __cmpxchg to __cmpxchg_32 to
> emphasize it's explicit support of 32bit data size with BUILD_BUG_ON()
> added to avoid any possible misuses with unsupported data types.
> 
> In case CONFIG_ARC_HAS_LLSC is undefined, arch_cmpxchg() uses spinlock
> to accomplish SMP-safety, so the BUILD_BUG_ON checking is uncecessary.
> 
> v2 -> v3:
>   - Patches regrouped and has the improvement for xtensa included
>   - Comments refined to address why these changes are needed
> 
> v1 -> v2:
>   - Try using native cmpxchg variants if avaialble, as Arnd advised
> 
> Signed-off-by: wuqiang.matt <wuqiang.matt@bytedance.com>
> Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> ---
>  arch/arc/include/asm/cmpxchg.h | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arc/include/asm/cmpxchg.h b/arch/arc/include/asm/cmpxchg.h
> index e138fde067de..bf46514f6f12 100644
> --- a/arch/arc/include/asm/cmpxchg.h
> +++ b/arch/arc/include/asm/cmpxchg.h
> @@ -18,14 +18,16 @@
>   * if (*ptr == @old)
>   *      *ptr = @new
>   */
> -#define __cmpxchg(ptr, old, new)					\
> +#define __cmpxchg_32(ptr, old, new)					\
>  ({									\
>  	__typeof__(*(ptr)) _prev;					\
>  									\
> +	BUILD_BUG_ON(sizeof(*(ptr)) != 4);				\
> +									\
>  	__asm__ __volatile__(						\
> -	"1:	llock  %0, [%1]	\n"					\
> +	"1:	llock  %0, [%1]		\n"				\
>  	"	brne   %0, %2, 2f	\n"				\
> -	"	scond  %3, [%1]	\n"					\
> +	"	scond  %3, [%1]		\n"				\
>  	"	bnz     1b		\n"				\
>  	"2:				\n"				\
>  	: "=&r"(_prev)	/* Early clobber prevent reg reuse */		\
> @@ -47,7 +49,7 @@
>  									\
>  	switch(sizeof((_p_))) {						\
>  	case 4:								\
> -		_prev_ = __cmpxchg(_p_, _o_, _n_);			\
> +		_prev_ = __cmpxchg_32(_p_, _o_, _n_);			\
>  		break;							\
>  	default:							\
>  		BUILD_BUG();						\
> @@ -65,8 +67,6 @@
>  	__typeof__(*(ptr)) _prev_;					\
>  	unsigned long __flags;						\
>  									\
> -	BUILD_BUG_ON(sizeof(_p_) != 4);					\
> -									\

I think I made some comments here that have not been addressed or
replied.

Thanks,
Andi

>  	/*								\
>  	 * spin lock/unlock provide the needed smp_mb() before/after	\
>  	 */								\
> -- 
> 2.40.1
wuqiang.matt Nov. 23, 2023, 12:06 a.m. UTC | #2 
Hello Andi,

On 2023/11/23 06:17, Andi Shyti wrote:
> Hi Wuqiang,
> 
> On Tue, Nov 21, 2023 at 10:23:43PM +0800, wuqiang.matt wrote:
>> arch_cmpxchg() should check data size rather than pointer size in case
>> CONFIG_ARC_HAS_LLSC is defined. So rename __cmpxchg to __cmpxchg_32 to
>> emphasize it's explicit support of 32bit data size with BUILD_BUG_ON()
>> added to avoid any possible misuses with unsupported data types.
>>
>> In case CONFIG_ARC_HAS_LLSC is undefined, arch_cmpxchg() uses spinlock
>> to accomplish SMP-safety, so the BUILD_BUG_ON checking is uncecessary.
>>
>> v2 -> v3:
>>    - Patches regrouped and has the improvement for xtensa included
>>    - Comments refined to address why these changes are needed
>>
>> v1 -> v2:
>>    - Try using native cmpxchg variants if avaialble, as Arnd advised

BTW, the changelog should be in the cover letter. I'll correct it in next
version, so don't bother resending to make more noises.

>> Signed-off-by: wuqiang.matt <wuqiang.matt@bytedance.com>
>> Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
>> ---
>>   arch/arc/include/asm/cmpxchg.h | 12 ++++++------
>>   1 file changed, 6 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/arc/include/asm/cmpxchg.h b/arch/arc/include/asm/cmpxchg.h
>> index e138fde067de..bf46514f6f12 100644
>> --- a/arch/arc/include/asm/cmpxchg.h
>> +++ b/arch/arc/include/asm/cmpxchg.h
>> @@ -18,14 +18,16 @@
>>    * if (*ptr == @old)
>>    *      *ptr = @new
>>    */
>> -#define __cmpxchg(ptr, old, new)					\
>> +#define __cmpxchg_32(ptr, old, new)					\
>>   ({									\
>>   	__typeof__(*(ptr)) _prev;					\
>>   									\
>> +	BUILD_BUG_ON(sizeof(*(ptr)) != 4);				\
>> +									\
>>   	__asm__ __volatile__(						\
>> -	"1:	llock  %0, [%1]	\n"					\
>> +	"1:	llock  %0, [%1]		\n"				\
>>   	"	brne   %0, %2, 2f	\n"				\
>> -	"	scond  %3, [%1]	\n"					\
>> +	"	scond  %3, [%1]		\n"				\
>>   	"	bnz     1b		\n"				\
>>   	"2:				\n"				\
>>   	: "=&r"(_prev)	/* Early clobber prevent reg reuse */		\
>> @@ -47,7 +49,7 @@
>>   									\
>>   	switch(sizeof((_p_))) {						\
>>   	case 4:								\
>> -		_prev_ = __cmpxchg(_p_, _o_, _n_);			\
>> +		_prev_ = __cmpxchg_32(_p_, _o_, _n_);			\
>>   		break;							\
>>   	default:							\
>>   		BUILD_BUG();						\
>> @@ -65,8 +67,6 @@
>>   	__typeof__(*(ptr)) _prev_;					\
>>   	unsigned long __flags;						\
>>   									\
>> -	BUILD_BUG_ON(sizeof(_p_) != 4);					\
>> -									\
> 
> I think I made some comments here that have not been addressed or
> replied.

Sorry that I haven't seen your message. Could you resend ? I rechecked
my mailbox and the mailing lists, but no luck.


> Thanks,
> Andi

Regards,
Wuqiang

> 
>>   	/*								\
>>   	 * spin lock/unlock provide the needed smp_mb() before/after	\
>>   	 */								\
>> -- 
>> 2.40.1
diff mbox series

Patch

diff --git a/arch/arc/include/asm/cmpxchg.h b/arch/arc/include/asm/cmpxchg.h
index e138fde067de..bf46514f6f12 100644
--- a/arch/arc/include/asm/cmpxchg.h
+++ b/arch/arc/include/asm/cmpxchg.h
@@ -18,14 +18,16 @@ 
  * if (*ptr == @old)
  *      *ptr = @new
  */
-#define __cmpxchg(ptr, old, new)					\
+#define __cmpxchg_32(ptr, old, new)					\
 ({									\
 	__typeof__(*(ptr)) _prev;					\
 									\
+	BUILD_BUG_ON(sizeof(*(ptr)) != 4);				\
+									\
 	__asm__ __volatile__(						\
-	"1:	llock  %0, [%1]	\n"					\
+	"1:	llock  %0, [%1]		\n"				\
 	"	brne   %0, %2, 2f	\n"				\
-	"	scond  %3, [%1]	\n"					\
+	"	scond  %3, [%1]		\n"				\
 	"	bnz     1b		\n"				\
 	"2:				\n"				\
 	: "=&r"(_prev)	/* Early clobber prevent reg reuse */		\
@@ -47,7 +49,7 @@ 
 									\
 	switch(sizeof((_p_))) {						\
 	case 4:								\
-		_prev_ = __cmpxchg(_p_, _o_, _n_);			\
+		_prev_ = __cmpxchg_32(_p_, _o_, _n_);			\
 		break;							\
 	default:							\
 		BUILD_BUG();						\
@@ -65,8 +67,6 @@ 
 	__typeof__(*(ptr)) _prev_;					\
 	unsigned long __flags;						\
 									\
-	BUILD_BUG_ON(sizeof(_p_) != 4);					\
-									\
 	/*								\
 	 * spin lock/unlock provide the needed smp_mb() before/after	\
 	 */								\