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* [PATCH 1/2] locking/xchg/alpha: Use smp_mb() in place of __ASM__MB
@ 2018-02-22  9:24 Andrea Parri
  2018-02-22 21:46 ` Paul E. McKenney
  2018-02-23  8:27 ` [tip:locking/urgent] locking/xchg/alpha: Clean up barrier usage by using " tip-bot for Andrea Parri
  0 siblings, 2 replies; 4+ messages in thread
From: Andrea Parri @ 2018-02-22  9:24 UTC (permalink / raw)
  To: Ingo Molnar, Peter Zijlstra
  Cc: Andrea Parri, Paul E . McKenney, Alan Stern, Ivan Kokshaysky,
	Matt Turner, Richard Henderson, linux-alpha, linux-kernel

Replace each occurrence of __ASM__MB with a (trailing) smp_mb() in
xchg(), cmpxchg(), and remove the now unused __ASM__MB definitions;
this improves readability, with no additional synchronization cost.

Suggested-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: linux-alpha@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
 arch/alpha/include/asm/cmpxchg.h |  6 ------
 arch/alpha/include/asm/xchg.h    | 16 ++++++++--------
 2 files changed, 8 insertions(+), 14 deletions(-)

diff --git a/arch/alpha/include/asm/cmpxchg.h b/arch/alpha/include/asm/cmpxchg.h
index 46ebf14aed4e5..8a2b331e43feb 100644
--- a/arch/alpha/include/asm/cmpxchg.h
+++ b/arch/alpha/include/asm/cmpxchg.h
@@ -6,7 +6,6 @@
  * Atomic exchange routines.
  */
 
-#define __ASM__MB
 #define ____xchg(type, args...)		__xchg ## type ## _local(args)
 #define ____cmpxchg(type, args...)	__cmpxchg ## type ## _local(args)
 #include <asm/xchg.h>
@@ -33,10 +32,6 @@
 	cmpxchg_local((ptr), (o), (n));					\
 })
 
-#ifdef CONFIG_SMP
-#undef __ASM__MB
-#define __ASM__MB	"\tmb\n"
-#endif
 #undef ____xchg
 #undef ____cmpxchg
 #define ____xchg(type, args...)		__xchg ##type(args)
@@ -64,7 +59,6 @@
 	cmpxchg((ptr), (o), (n));					\
 })
 
-#undef __ASM__MB
 #undef ____cmpxchg
 
 #endif /* _ALPHA_CMPXCHG_H */
diff --git a/arch/alpha/include/asm/xchg.h b/arch/alpha/include/asm/xchg.h
index e2660866ce972..e1facf6fc2446 100644
--- a/arch/alpha/include/asm/xchg.h
+++ b/arch/alpha/include/asm/xchg.h
@@ -28,12 +28,12 @@ ____xchg(_u8, volatile char *m, unsigned long val)
 	"	or	%1,%2,%2\n"
 	"	stq_c	%2,0(%3)\n"
 	"	beq	%2,2f\n"
-		__ASM__MB
 	".subsection 2\n"
 	"2:	br	1b\n"
 	".previous"
 	: "=&r" (ret), "=&r" (val), "=&r" (tmp), "=&r" (addr64)
 	: "r" ((long)m), "1" (val) : "memory");
+	smp_mb();
 
 	return ret;
 }
@@ -52,12 +52,12 @@ ____xchg(_u16, volatile short *m, unsigned long val)
 	"	or	%1,%2,%2\n"
 	"	stq_c	%2,0(%3)\n"
 	"	beq	%2,2f\n"
-		__ASM__MB
 	".subsection 2\n"
 	"2:	br	1b\n"
 	".previous"
 	: "=&r" (ret), "=&r" (val), "=&r" (tmp), "=&r" (addr64)
 	: "r" ((long)m), "1" (val) : "memory");
+	smp_mb();
 
 	return ret;
 }
@@ -72,12 +72,12 @@ ____xchg(_u32, volatile int *m, unsigned long val)
 	"	bis $31,%3,%1\n"
 	"	stl_c %1,%2\n"
 	"	beq %1,2f\n"
-		__ASM__MB
 	".subsection 2\n"
 	"2:	br 1b\n"
 	".previous"
 	: "=&r" (val), "=&r" (dummy), "=m" (*m)
 	: "rI" (val), "m" (*m) : "memory");
+	smp_mb();
 
 	return val;
 }
@@ -92,12 +92,12 @@ ____xchg(_u64, volatile long *m, unsigned long val)
 	"	bis $31,%3,%1\n"
 	"	stq_c %1,%2\n"
 	"	beq %1,2f\n"
-		__ASM__MB
 	".subsection 2\n"
 	"2:	br 1b\n"
 	".previous"
 	: "=&r" (val), "=&r" (dummy), "=m" (*m)
 	: "rI" (val), "m" (*m) : "memory");
+	smp_mb();
 
 	return val;
 }
@@ -150,12 +150,12 @@ ____cmpxchg(_u8, volatile char *m, unsigned char old, unsigned char new)
 	"	stq_c	%2,0(%4)\n"
 	"	beq	%2,3f\n"
 	"2:\n"
-		__ASM__MB
 	".subsection 2\n"
 	"3:	br	1b\n"
 	".previous"
 	: "=&r" (prev), "=&r" (new), "=&r" (tmp), "=&r" (cmp), "=&r" (addr64)
 	: "r" ((long)m), "Ir" (old), "1" (new) : "memory");
+	smp_mb();
 
 	return prev;
 }
@@ -177,12 +177,12 @@ ____cmpxchg(_u16, volatile short *m, unsigned short old, unsigned short new)
 	"	stq_c	%2,0(%4)\n"
 	"	beq	%2,3f\n"
 	"2:\n"
-		__ASM__MB
 	".subsection 2\n"
 	"3:	br	1b\n"
 	".previous"
 	: "=&r" (prev), "=&r" (new), "=&r" (tmp), "=&r" (cmp), "=&r" (addr64)
 	: "r" ((long)m), "Ir" (old), "1" (new) : "memory");
+	smp_mb();
 
 	return prev;
 }
@@ -200,12 +200,12 @@ ____cmpxchg(_u32, volatile int *m, int old, int new)
 	"	stl_c %1,%2\n"
 	"	beq %1,3f\n"
 	"2:\n"
-		__ASM__MB
 	".subsection 2\n"
 	"3:	br 1b\n"
 	".previous"
 	: "=&r"(prev), "=&r"(cmp), "=m"(*m)
 	: "r"((long) old), "r"(new), "m"(*m) : "memory");
+	smp_mb();
 
 	return prev;
 }
@@ -223,12 +223,12 @@ ____cmpxchg(_u64, volatile long *m, unsigned long old, unsigned long new)
 	"	stq_c %1,%2\n"
 	"	beq %1,3f\n"
 	"2:\n"
-		__ASM__MB
 	".subsection 2\n"
 	"3:	br 1b\n"
 	".previous"
 	: "=&r"(prev), "=&r"(cmp), "=m"(*m)
 	: "r"((long) old), "r"(new), "m"(*m) : "memory");
+	smp_mb();
 
 	return prev;
 }
-- 
2.7.4

^ permalink raw reply related	[flat|nested] 4+ messages in thread

* Re: [PATCH 1/2] locking/xchg/alpha: Use smp_mb() in place of __ASM__MB
  2018-02-22  9:24 [PATCH 1/2] locking/xchg/alpha: Use smp_mb() in place of __ASM__MB Andrea Parri
@ 2018-02-22 21:46 ` Paul E. McKenney
  2018-02-23  8:27 ` [tip:locking/urgent] locking/xchg/alpha: Clean up barrier usage by using " tip-bot for Andrea Parri
  1 sibling, 0 replies; 4+ messages in thread
From: Paul E. McKenney @ 2018-02-22 21:46 UTC (permalink / raw)
  To: Andrea Parri
  Cc: Ingo Molnar, Peter Zijlstra, Alan Stern, Ivan Kokshaysky,
	Matt Turner, Richard Henderson, linux-alpha, linux-kernel

On Thu, Feb 22, 2018 at 10:24:29AM +0100, Andrea Parri wrote:
> Replace each occurrence of __ASM__MB with a (trailing) smp_mb() in
> xchg(), cmpxchg(), and remove the now unused __ASM__MB definitions;
> this improves readability, with no additional synchronization cost.
> 
> Suggested-by: Will Deacon <will.deacon@arm.com>
> Signed-off-by: Andrea Parri <parri.andrea@gmail.com>

I am a bit confused by the use of out-of-line branches to do a backwards
branch, but those were in place to start with.  Maybe the point is to
defeat backwards-branch prediction or some such.

Regardless...

Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Cc: Alan Stern <stern@rowland.harvard.edu>
> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
> Cc: Matt Turner <mattst88@gmail.com>
> Cc: Richard Henderson <rth@twiddle.net>
> Cc: linux-alpha@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> ---
>  arch/alpha/include/asm/cmpxchg.h |  6 ------
>  arch/alpha/include/asm/xchg.h    | 16 ++++++++--------
>  2 files changed, 8 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/alpha/include/asm/cmpxchg.h b/arch/alpha/include/asm/cmpxchg.h
> index 46ebf14aed4e5..8a2b331e43feb 100644
> --- a/arch/alpha/include/asm/cmpxchg.h
> +++ b/arch/alpha/include/asm/cmpxchg.h
> @@ -6,7 +6,6 @@
>   * Atomic exchange routines.
>   */
> 
> -#define __ASM__MB
>  #define ____xchg(type, args...)		__xchg ## type ## _local(args)
>  #define ____cmpxchg(type, args...)	__cmpxchg ## type ## _local(args)
>  #include <asm/xchg.h>
> @@ -33,10 +32,6 @@
>  	cmpxchg_local((ptr), (o), (n));					\
>  })
> 
> -#ifdef CONFIG_SMP
> -#undef __ASM__MB
> -#define __ASM__MB	"\tmb\n"
> -#endif
>  #undef ____xchg
>  #undef ____cmpxchg
>  #define ____xchg(type, args...)		__xchg ##type(args)
> @@ -64,7 +59,6 @@
>  	cmpxchg((ptr), (o), (n));					\
>  })
> 
> -#undef __ASM__MB
>  #undef ____cmpxchg
> 
>  #endif /* _ALPHA_CMPXCHG_H */
> diff --git a/arch/alpha/include/asm/xchg.h b/arch/alpha/include/asm/xchg.h
> index e2660866ce972..e1facf6fc2446 100644
> --- a/arch/alpha/include/asm/xchg.h
> +++ b/arch/alpha/include/asm/xchg.h
> @@ -28,12 +28,12 @@ ____xchg(_u8, volatile char *m, unsigned long val)
>  	"	or	%1,%2,%2\n"
>  	"	stq_c	%2,0(%3)\n"
>  	"	beq	%2,2f\n"
> -		__ASM__MB
>  	".subsection 2\n"
>  	"2:	br	1b\n"
>  	".previous"
>  	: "=&r" (ret), "=&r" (val), "=&r" (tmp), "=&r" (addr64)
>  	: "r" ((long)m), "1" (val) : "memory");
> +	smp_mb();
> 
>  	return ret;
>  }
> @@ -52,12 +52,12 @@ ____xchg(_u16, volatile short *m, unsigned long val)
>  	"	or	%1,%2,%2\n"
>  	"	stq_c	%2,0(%3)\n"
>  	"	beq	%2,2f\n"
> -		__ASM__MB
>  	".subsection 2\n"
>  	"2:	br	1b\n"
>  	".previous"
>  	: "=&r" (ret), "=&r" (val), "=&r" (tmp), "=&r" (addr64)
>  	: "r" ((long)m), "1" (val) : "memory");
> +	smp_mb();
> 
>  	return ret;
>  }
> @@ -72,12 +72,12 @@ ____xchg(_u32, volatile int *m, unsigned long val)
>  	"	bis $31,%3,%1\n"
>  	"	stl_c %1,%2\n"
>  	"	beq %1,2f\n"
> -		__ASM__MB
>  	".subsection 2\n"
>  	"2:	br 1b\n"
>  	".previous"
>  	: "=&r" (val), "=&r" (dummy), "=m" (*m)
>  	: "rI" (val), "m" (*m) : "memory");
> +	smp_mb();
> 
>  	return val;
>  }
> @@ -92,12 +92,12 @@ ____xchg(_u64, volatile long *m, unsigned long val)
>  	"	bis $31,%3,%1\n"
>  	"	stq_c %1,%2\n"
>  	"	beq %1,2f\n"
> -		__ASM__MB
>  	".subsection 2\n"
>  	"2:	br 1b\n"
>  	".previous"
>  	: "=&r" (val), "=&r" (dummy), "=m" (*m)
>  	: "rI" (val), "m" (*m) : "memory");
> +	smp_mb();
> 
>  	return val;
>  }
> @@ -150,12 +150,12 @@ ____cmpxchg(_u8, volatile char *m, unsigned char old, unsigned char new)
>  	"	stq_c	%2,0(%4)\n"
>  	"	beq	%2,3f\n"
>  	"2:\n"
> -		__ASM__MB
>  	".subsection 2\n"
>  	"3:	br	1b\n"
>  	".previous"
>  	: "=&r" (prev), "=&r" (new), "=&r" (tmp), "=&r" (cmp), "=&r" (addr64)
>  	: "r" ((long)m), "Ir" (old), "1" (new) : "memory");
> +	smp_mb();
> 
>  	return prev;
>  }
> @@ -177,12 +177,12 @@ ____cmpxchg(_u16, volatile short *m, unsigned short old, unsigned short new)
>  	"	stq_c	%2,0(%4)\n"
>  	"	beq	%2,3f\n"
>  	"2:\n"
> -		__ASM__MB
>  	".subsection 2\n"
>  	"3:	br	1b\n"
>  	".previous"
>  	: "=&r" (prev), "=&r" (new), "=&r" (tmp), "=&r" (cmp), "=&r" (addr64)
>  	: "r" ((long)m), "Ir" (old), "1" (new) : "memory");
> +	smp_mb();
> 
>  	return prev;
>  }
> @@ -200,12 +200,12 @@ ____cmpxchg(_u32, volatile int *m, int old, int new)
>  	"	stl_c %1,%2\n"
>  	"	beq %1,3f\n"
>  	"2:\n"
> -		__ASM__MB
>  	".subsection 2\n"
>  	"3:	br 1b\n"
>  	".previous"
>  	: "=&r"(prev), "=&r"(cmp), "=m"(*m)
>  	: "r"((long) old), "r"(new), "m"(*m) : "memory");
> +	smp_mb();
> 
>  	return prev;
>  }
> @@ -223,12 +223,12 @@ ____cmpxchg(_u64, volatile long *m, unsigned long old, unsigned long new)
>  	"	stq_c %1,%2\n"
>  	"	beq %1,3f\n"
>  	"2:\n"
> -		__ASM__MB
>  	".subsection 2\n"
>  	"3:	br 1b\n"
>  	".previous"
>  	: "=&r"(prev), "=&r"(cmp), "=m"(*m)
>  	: "r"((long) old), "r"(new), "m"(*m) : "memory");
> +	smp_mb();
> 
>  	return prev;
>  }
> -- 
> 2.7.4
> 

^ permalink raw reply	[flat|nested] 4+ messages in thread

* [tip:locking/urgent] locking/xchg/alpha: Clean up barrier usage by using smp_mb() in place of __ASM__MB
  2018-02-22  9:24 [PATCH 1/2] locking/xchg/alpha: Use smp_mb() in place of __ASM__MB Andrea Parri
  2018-02-22 21:46 ` Paul E. McKenney
@ 2018-02-23  8:27 ` tip-bot for Andrea Parri
  2018-02-26 18:05   ` Will Deacon
  1 sibling, 1 reply; 4+ messages in thread
From: tip-bot for Andrea Parri @ 2018-02-23  8:27 UTC (permalink / raw)
  To: linux-tip-commits
  Cc: will.deacon, rth, mattst88, tglx, hpa, parri.andrea, ink, stern,
	paulmck, mingo, linux-kernel, peterz, torvalds, akpm

Commit-ID:  79d442461df7478cdd0c50d9b8a76f431f150fa3
Gitweb:     https://git.kernel.org/tip/79d442461df7478cdd0c50d9b8a76f431f150fa3
Author:     Andrea Parri <parri.andrea@gmail.com>
AuthorDate: Thu, 22 Feb 2018 10:24:29 +0100
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 23 Feb 2018 08:38:15 +0100

locking/xchg/alpha: Clean up barrier usage by using smp_mb() in place of __ASM__MB

Replace each occurrence of __ASM__MB with a (trailing) smp_mb() in
xchg(), cmpxchg(), and remove the now unused __ASM__MB definitions;
this improves readability, with no additional synchronization cost.

Suggested-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-alpha@vger.kernel.org
Link: http://lkml.kernel.org/r/1519291469-5702-1-git-send-email-parri.andrea@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/alpha/include/asm/cmpxchg.h |  6 ------
 arch/alpha/include/asm/xchg.h    | 16 ++++++++--------
 2 files changed, 8 insertions(+), 14 deletions(-)

diff --git a/arch/alpha/include/asm/cmpxchg.h b/arch/alpha/include/asm/cmpxchg.h
index 46ebf14aed4e..8a2b331e43fe 100644
--- a/arch/alpha/include/asm/cmpxchg.h
+++ b/arch/alpha/include/asm/cmpxchg.h
@@ -6,7 +6,6 @@
  * Atomic exchange routines.
  */
 
-#define __ASM__MB
 #define ____xchg(type, args...)		__xchg ## type ## _local(args)
 #define ____cmpxchg(type, args...)	__cmpxchg ## type ## _local(args)
 #include <asm/xchg.h>
@@ -33,10 +32,6 @@
 	cmpxchg_local((ptr), (o), (n));					\
 })
 
-#ifdef CONFIG_SMP
-#undef __ASM__MB
-#define __ASM__MB	"\tmb\n"
-#endif
 #undef ____xchg
 #undef ____cmpxchg
 #define ____xchg(type, args...)		__xchg ##type(args)
@@ -64,7 +59,6 @@
 	cmpxchg((ptr), (o), (n));					\
 })
 
-#undef __ASM__MB
 #undef ____cmpxchg
 
 #endif /* _ALPHA_CMPXCHG_H */
diff --git a/arch/alpha/include/asm/xchg.h b/arch/alpha/include/asm/xchg.h
index e2660866ce97..e1facf6fc244 100644
--- a/arch/alpha/include/asm/xchg.h
+++ b/arch/alpha/include/asm/xchg.h
@@ -28,12 +28,12 @@ ____xchg(_u8, volatile char *m, unsigned long val)
 	"	or	%1,%2,%2\n"
 	"	stq_c	%2,0(%3)\n"
 	"	beq	%2,2f\n"
-		__ASM__MB
 	".subsection 2\n"
 	"2:	br	1b\n"
 	".previous"
 	: "=&r" (ret), "=&r" (val), "=&r" (tmp), "=&r" (addr64)
 	: "r" ((long)m), "1" (val) : "memory");
+	smp_mb();
 
 	return ret;
 }
@@ -52,12 +52,12 @@ ____xchg(_u16, volatile short *m, unsigned long val)
 	"	or	%1,%2,%2\n"
 	"	stq_c	%2,0(%3)\n"
 	"	beq	%2,2f\n"
-		__ASM__MB
 	".subsection 2\n"
 	"2:	br	1b\n"
 	".previous"
 	: "=&r" (ret), "=&r" (val), "=&r" (tmp), "=&r" (addr64)
 	: "r" ((long)m), "1" (val) : "memory");
+	smp_mb();
 
 	return ret;
 }
@@ -72,12 +72,12 @@ ____xchg(_u32, volatile int *m, unsigned long val)
 	"	bis $31,%3,%1\n"
 	"	stl_c %1,%2\n"
 	"	beq %1,2f\n"
-		__ASM__MB
 	".subsection 2\n"
 	"2:	br 1b\n"
 	".previous"
 	: "=&r" (val), "=&r" (dummy), "=m" (*m)
 	: "rI" (val), "m" (*m) : "memory");
+	smp_mb();
 
 	return val;
 }
@@ -92,12 +92,12 @@ ____xchg(_u64, volatile long *m, unsigned long val)
 	"	bis $31,%3,%1\n"
 	"	stq_c %1,%2\n"
 	"	beq %1,2f\n"
-		__ASM__MB
 	".subsection 2\n"
 	"2:	br 1b\n"
 	".previous"
 	: "=&r" (val), "=&r" (dummy), "=m" (*m)
 	: "rI" (val), "m" (*m) : "memory");
+	smp_mb();
 
 	return val;
 }
@@ -150,12 +150,12 @@ ____cmpxchg(_u8, volatile char *m, unsigned char old, unsigned char new)
 	"	stq_c	%2,0(%4)\n"
 	"	beq	%2,3f\n"
 	"2:\n"
-		__ASM__MB
 	".subsection 2\n"
 	"3:	br	1b\n"
 	".previous"
 	: "=&r" (prev), "=&r" (new), "=&r" (tmp), "=&r" (cmp), "=&r" (addr64)
 	: "r" ((long)m), "Ir" (old), "1" (new) : "memory");
+	smp_mb();
 
 	return prev;
 }
@@ -177,12 +177,12 @@ ____cmpxchg(_u16, volatile short *m, unsigned short old, unsigned short new)
 	"	stq_c	%2,0(%4)\n"
 	"	beq	%2,3f\n"
 	"2:\n"
-		__ASM__MB
 	".subsection 2\n"
 	"3:	br	1b\n"
 	".previous"
 	: "=&r" (prev), "=&r" (new), "=&r" (tmp), "=&r" (cmp), "=&r" (addr64)
 	: "r" ((long)m), "Ir" (old), "1" (new) : "memory");
+	smp_mb();
 
 	return prev;
 }
@@ -200,12 +200,12 @@ ____cmpxchg(_u32, volatile int *m, int old, int new)
 	"	stl_c %1,%2\n"
 	"	beq %1,3f\n"
 	"2:\n"
-		__ASM__MB
 	".subsection 2\n"
 	"3:	br 1b\n"
 	".previous"
 	: "=&r"(prev), "=&r"(cmp), "=m"(*m)
 	: "r"((long) old), "r"(new), "m"(*m) : "memory");
+	smp_mb();
 
 	return prev;
 }
@@ -223,12 +223,12 @@ ____cmpxchg(_u64, volatile long *m, unsigned long old, unsigned long new)
 	"	stq_c %1,%2\n"
 	"	beq %1,3f\n"
 	"2:\n"
-		__ASM__MB
 	".subsection 2\n"
 	"3:	br 1b\n"
 	".previous"
 	: "=&r"(prev), "=&r"(cmp), "=m"(*m)
 	: "r"((long) old), "r"(new), "m"(*m) : "memory");
+	smp_mb();
 
 	return prev;
 }

^ permalink raw reply related	[flat|nested] 4+ messages in thread

* Re: [tip:locking/urgent] locking/xchg/alpha: Clean up barrier usage by using smp_mb() in place of __ASM__MB
  2018-02-23  8:27 ` [tip:locking/urgent] locking/xchg/alpha: Clean up barrier usage by using " tip-bot for Andrea Parri
@ 2018-02-26 18:05   ` Will Deacon
  0 siblings, 0 replies; 4+ messages in thread
From: Will Deacon @ 2018-02-26 18:05 UTC (permalink / raw)
  To: mattst88, rth, tglx, hpa, stern, parri.andrea, ink, akpm,
	paulmck, torvalds, linux-kernel, peterz, mingo
  Cc: linux-tip-commits

Hi Andrea,

I know this is in mainline now, but I think the way you've got the barriers
here:

On Fri, Feb 23, 2018 at 12:27:54AM -0800, tip-bot for Andrea Parri wrote:
> diff --git a/arch/alpha/include/asm/cmpxchg.h b/arch/alpha/include/asm/cmpxchg.h
> index 46ebf14aed4e..8a2b331e43fe 100644
> --- a/arch/alpha/include/asm/cmpxchg.h
> +++ b/arch/alpha/include/asm/cmpxchg.h
> @@ -6,7 +6,6 @@
>   * Atomic exchange routines.
>   */
>  
> -#define __ASM__MB
>  #define ____xchg(type, args...)		__xchg ## type ## _local(args)
>  #define ____cmpxchg(type, args...)	__cmpxchg ## type ## _local(args)
>  #include <asm/xchg.h>
> @@ -33,10 +32,6 @@
>  	cmpxchg_local((ptr), (o), (n));					\
>  })
>  
> -#ifdef CONFIG_SMP
> -#undef __ASM__MB
> -#define __ASM__MB	"\tmb\n"
> -#endif
>  #undef ____xchg
>  #undef ____cmpxchg
>  #define ____xchg(type, args...)		__xchg ##type(args)
> @@ -64,7 +59,6 @@
>  	cmpxchg((ptr), (o), (n));					\
>  })
>  
> -#undef __ASM__MB
>  #undef ____cmpxchg
>  
>  #endif /* _ALPHA_CMPXCHG_H */
> diff --git a/arch/alpha/include/asm/xchg.h b/arch/alpha/include/asm/xchg.h
> index e2660866ce97..e1facf6fc244 100644
> --- a/arch/alpha/include/asm/xchg.h
> +++ b/arch/alpha/include/asm/xchg.h
> @@ -28,12 +28,12 @@ ____xchg(_u8, volatile char *m, unsigned long val)
>  	"	or	%1,%2,%2\n"
>  	"	stq_c	%2,0(%3)\n"
>  	"	beq	%2,2f\n"
> -		__ASM__MB
>  	".subsection 2\n"
>  	"2:	br	1b\n"
>  	".previous"
>  	: "=&r" (ret), "=&r" (val), "=&r" (tmp), "=&r" (addr64)
>  	: "r" ((long)m), "1" (val) : "memory");
> +	smp_mb();
>  
>  	return ret;

ends up adding unnecessary barriers to the _local variants, which the
previous code took care to avoid. That's why I suggesting adding
the smp_mb() into the cmpxchg macro rather than the ____cmpxchg variants.

I think it's worth spinning another patch to fix this properly.

Will

^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2018-02-26 18:05 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-02-22  9:24 [PATCH 1/2] locking/xchg/alpha: Use smp_mb() in place of __ASM__MB Andrea Parri
2018-02-22 21:46 ` Paul E. McKenney
2018-02-23  8:27 ` [tip:locking/urgent] locking/xchg/alpha: Clean up barrier usage by using " tip-bot for Andrea Parri
2018-02-26 18:05   ` Will Deacon

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