* [PATCH] locking/xchg/alpha: Remove memory barriers from the _local() variants
@ 2018-02-27 4:00 Andrea Parri
2018-02-27 20:08 ` Andrea Parri
2018-03-12 12:17 ` [tip:locking/core] locking/xchg/alpha: Remove superfluous " tip-bot for Andrea Parri
0 siblings, 2 replies; 5+ messages in thread
From: Andrea Parri @ 2018-02-27 4:00 UTC (permalink / raw)
To: Ingo Molnar, Peter Zijlstra
Cc: linux-kernel, Andrea Parri, Paul E . McKenney, Alan Stern,
Andrew Morton, Ivan Kokshaysky, Linus Torvalds, Matt Turner,
Richard Henderson, Thomas Gleixner, linux-alpha
Commits 79d442461df74 ("locking/xchg/alpha: Clean up barrier usage by using
smp_mb() in place of __ASM__MB") and 472e8c55cf662 ("locking/xchg/alpha:
Fix xchg() and cmpxchg() memory ordering bugs") ended up adding unnecessary
barriers to the _local variants, which the previous code took care to avoid.
Fix them by adding the smp_mb() into the cmpxchg macro rather than into the
____cmpxchg variants.
Fixes: 79d442461df74 ("locking/xchg/alpha: Clean up barrier usage by using smp_mb() in place of __ASM__MB")
Fixes: 472e8c55cf662 ("locking/xchg/alpha: Fix xchg() and cmpxchg() memory ordering bugs")
Reported-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
Cc: 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
---
arch/alpha/include/asm/cmpxchg.h | 20 ++++++++++++++++----
arch/alpha/include/asm/xchg.h | 27 ---------------------------
2 files changed, 16 insertions(+), 31 deletions(-)
diff --git a/arch/alpha/include/asm/cmpxchg.h b/arch/alpha/include/asm/cmpxchg.h
index 8a2b331e43feb..6c7c394524714 100644
--- a/arch/alpha/include/asm/cmpxchg.h
+++ b/arch/alpha/include/asm/cmpxchg.h
@@ -38,19 +38,31 @@
#define ____cmpxchg(type, args...) __cmpxchg ##type(args)
#include <asm/xchg.h>
+/*
+ * The leading and the trailing memory barriers guarantee that these
+ * operations are fully ordered.
+ */
#define xchg(ptr, x) \
({ \
+ __typeof__(*(ptr)) __ret; \
__typeof__(*(ptr)) _x_ = (x); \
- (__typeof__(*(ptr))) __xchg((ptr), (unsigned long)_x_, \
- sizeof(*(ptr))); \
+ smp_mb(); \
+ __ret = (__typeof__(*(ptr))) \
+ __xchg((ptr), (unsigned long)_x_, sizeof(*(ptr))); \
+ smp_mb(); \
+ __ret; \
})
#define cmpxchg(ptr, o, n) \
({ \
+ __typeof__(*(ptr)) __ret; \
__typeof__(*(ptr)) _o_ = (o); \
__typeof__(*(ptr)) _n_ = (n); \
- (__typeof__(*(ptr))) __cmpxchg((ptr), (unsigned long)_o_, \
- (unsigned long)_n_, sizeof(*(ptr)));\
+ smp_mb(); \
+ __ret = (__typeof__(*(ptr))) __cmpxchg((ptr), \
+ (unsigned long)_o_, (unsigned long)_n_, sizeof(*(ptr)));\
+ smp_mb(); \
+ __ret; \
})
#define cmpxchg64(ptr, o, n) \
diff --git a/arch/alpha/include/asm/xchg.h b/arch/alpha/include/asm/xchg.h
index e2b59fac5257d..7adb80c6746ac 100644
--- a/arch/alpha/include/asm/xchg.h
+++ b/arch/alpha/include/asm/xchg.h
@@ -12,10 +12,6 @@
* Atomic exchange.
* Since it can be used to implement critical sections
* it must clobber "memory" (also for interrupts in UP).
- *
- * The leading and the trailing memory barriers guarantee that these
- * operations are fully ordered.
- *
*/
static inline unsigned long
@@ -23,7 +19,6 @@ ____xchg(_u8, volatile char *m, unsigned long val)
{
unsigned long ret, tmp, addr64;
- smp_mb();
__asm__ __volatile__(
" andnot %4,7,%3\n"
" insbl %1,%4,%1\n"
@@ -38,7 +33,6 @@ ____xchg(_u8, volatile char *m, unsigned long val)
".previous"
: "=&r" (ret), "=&r" (val), "=&r" (tmp), "=&r" (addr64)
: "r" ((long)m), "1" (val) : "memory");
- smp_mb();
return ret;
}
@@ -48,7 +42,6 @@ ____xchg(_u16, volatile short *m, unsigned long val)
{
unsigned long ret, tmp, addr64;
- smp_mb();
__asm__ __volatile__(
" andnot %4,7,%3\n"
" inswl %1,%4,%1\n"
@@ -63,7 +56,6 @@ ____xchg(_u16, volatile short *m, unsigned long val)
".previous"
: "=&r" (ret), "=&r" (val), "=&r" (tmp), "=&r" (addr64)
: "r" ((long)m), "1" (val) : "memory");
- smp_mb();
return ret;
}
@@ -73,7 +65,6 @@ ____xchg(_u32, volatile int *m, unsigned long val)
{
unsigned long dummy;
- smp_mb();
__asm__ __volatile__(
"1: ldl_l %0,%4\n"
" bis $31,%3,%1\n"
@@ -84,7 +75,6 @@ ____xchg(_u32, volatile int *m, unsigned long val)
".previous"
: "=&r" (val), "=&r" (dummy), "=m" (*m)
: "rI" (val), "m" (*m) : "memory");
- smp_mb();
return val;
}
@@ -94,7 +84,6 @@ ____xchg(_u64, volatile long *m, unsigned long val)
{
unsigned long dummy;
- smp_mb();
__asm__ __volatile__(
"1: ldq_l %0,%4\n"
" bis $31,%3,%1\n"
@@ -105,7 +94,6 @@ ____xchg(_u64, volatile long *m, unsigned long val)
".previous"
: "=&r" (val), "=&r" (dummy), "=m" (*m)
: "rI" (val), "m" (*m) : "memory");
- smp_mb();
return val;
}
@@ -135,13 +123,6 @@ ____xchg(, volatile void *ptr, unsigned long x, int size)
* Atomic compare and exchange. Compare OLD with MEM, if identical,
* store NEW in MEM. Return the initial value in MEM. Success is
* indicated by comparing RETURN with OLD.
- *
- * The leading and the trailing memory barriers guarantee that these
- * operations are fully ordered.
- *
- * The trailing memory barrier is placed in SMP unconditionally, in
- * order to guarantee that dependency ordering is preserved when a
- * dependency is headed by an unsuccessful operation.
*/
static inline unsigned long
@@ -149,7 +130,6 @@ ____cmpxchg(_u8, volatile char *m, unsigned char old, unsigned char new)
{
unsigned long prev, tmp, cmp, addr64;
- smp_mb();
__asm__ __volatile__(
" andnot %5,7,%4\n"
" insbl %1,%5,%1\n"
@@ -167,7 +147,6 @@ ____cmpxchg(_u8, volatile char *m, unsigned char old, unsigned char new)
".previous"
: "=&r" (prev), "=&r" (new), "=&r" (tmp), "=&r" (cmp), "=&r" (addr64)
: "r" ((long)m), "Ir" (old), "1" (new) : "memory");
- smp_mb();
return prev;
}
@@ -177,7 +156,6 @@ ____cmpxchg(_u16, volatile short *m, unsigned short old, unsigned short new)
{
unsigned long prev, tmp, cmp, addr64;
- smp_mb();
__asm__ __volatile__(
" andnot %5,7,%4\n"
" inswl %1,%5,%1\n"
@@ -195,7 +173,6 @@ ____cmpxchg(_u16, volatile short *m, unsigned short old, unsigned short new)
".previous"
: "=&r" (prev), "=&r" (new), "=&r" (tmp), "=&r" (cmp), "=&r" (addr64)
: "r" ((long)m), "Ir" (old), "1" (new) : "memory");
- smp_mb();
return prev;
}
@@ -205,7 +182,6 @@ ____cmpxchg(_u32, volatile int *m, int old, int new)
{
unsigned long prev, cmp;
- smp_mb();
__asm__ __volatile__(
"1: ldl_l %0,%5\n"
" cmpeq %0,%3,%1\n"
@@ -219,7 +195,6 @@ ____cmpxchg(_u32, volatile int *m, int old, int new)
".previous"
: "=&r"(prev), "=&r"(cmp), "=m"(*m)
: "r"((long) old), "r"(new), "m"(*m) : "memory");
- smp_mb();
return prev;
}
@@ -229,7 +204,6 @@ ____cmpxchg(_u64, volatile long *m, unsigned long old, unsigned long new)
{
unsigned long prev, cmp;
- smp_mb();
__asm__ __volatile__(
"1: ldq_l %0,%5\n"
" cmpeq %0,%3,%1\n"
@@ -243,7 +217,6 @@ ____cmpxchg(_u64, volatile long *m, unsigned long old, unsigned long new)
".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] 5+ messages in thread* Re: [PATCH] locking/xchg/alpha: Remove memory barriers from the _local() variants
2018-02-27 4:00 [PATCH] locking/xchg/alpha: Remove memory barriers from the _local() variants Andrea Parri
@ 2018-02-27 20:08 ` Andrea Parri
2018-02-28 10:58 ` Will Deacon
2018-03-12 12:17 ` [tip:locking/core] locking/xchg/alpha: Remove superfluous " tip-bot for Andrea Parri
1 sibling, 1 reply; 5+ messages in thread
From: Andrea Parri @ 2018-02-27 20:08 UTC (permalink / raw)
To: Ingo Molnar, Peter Zijlstra
Cc: linux-kernel, Paul E . McKenney, Alan Stern, Andrew Morton,
Ivan Kokshaysky, Linus Torvalds, Matt Turner, Richard Henderson,
Thomas Gleixner, linux-alpha, will.deacon
[+ Will]
I'm not sure how this happened; Will, you at least figure as Reported-by: ;-)
Andrea
On Tue, Feb 27, 2018 at 05:00:58AM +0100, Andrea Parri wrote:
> Commits 79d442461df74 ("locking/xchg/alpha: Clean up barrier usage by using
> smp_mb() in place of __ASM__MB") and 472e8c55cf662 ("locking/xchg/alpha:
> Fix xchg() and cmpxchg() memory ordering bugs") ended up adding unnecessary
> barriers to the _local variants, which the previous code took care to avoid.
>
> Fix them by adding the smp_mb() into the cmpxchg macro rather than into the
> ____cmpxchg variants.
>
> Fixes: 79d442461df74 ("locking/xchg/alpha: Clean up barrier usage by using smp_mb() in place of __ASM__MB")
> Fixes: 472e8c55cf662 ("locking/xchg/alpha: Fix xchg() and cmpxchg() memory ordering bugs")
> Reported-by: Will Deacon <will.deacon@arm.com>
> Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
> Cc: 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
> ---
> arch/alpha/include/asm/cmpxchg.h | 20 ++++++++++++++++----
> arch/alpha/include/asm/xchg.h | 27 ---------------------------
> 2 files changed, 16 insertions(+), 31 deletions(-)
>
> diff --git a/arch/alpha/include/asm/cmpxchg.h b/arch/alpha/include/asm/cmpxchg.h
> index 8a2b331e43feb..6c7c394524714 100644
> --- a/arch/alpha/include/asm/cmpxchg.h
> +++ b/arch/alpha/include/asm/cmpxchg.h
> @@ -38,19 +38,31 @@
> #define ____cmpxchg(type, args...) __cmpxchg ##type(args)
> #include <asm/xchg.h>
>
> +/*
> + * The leading and the trailing memory barriers guarantee that these
> + * operations are fully ordered.
> + */
> #define xchg(ptr, x) \
> ({ \
> + __typeof__(*(ptr)) __ret; \
> __typeof__(*(ptr)) _x_ = (x); \
> - (__typeof__(*(ptr))) __xchg((ptr), (unsigned long)_x_, \
> - sizeof(*(ptr))); \
> + smp_mb(); \
> + __ret = (__typeof__(*(ptr))) \
> + __xchg((ptr), (unsigned long)_x_, sizeof(*(ptr))); \
> + smp_mb(); \
> + __ret; \
> })
>
> #define cmpxchg(ptr, o, n) \
> ({ \
> + __typeof__(*(ptr)) __ret; \
> __typeof__(*(ptr)) _o_ = (o); \
> __typeof__(*(ptr)) _n_ = (n); \
> - (__typeof__(*(ptr))) __cmpxchg((ptr), (unsigned long)_o_, \
> - (unsigned long)_n_, sizeof(*(ptr)));\
> + smp_mb(); \
> + __ret = (__typeof__(*(ptr))) __cmpxchg((ptr), \
> + (unsigned long)_o_, (unsigned long)_n_, sizeof(*(ptr)));\
> + smp_mb(); \
> + __ret; \
> })
>
> #define cmpxchg64(ptr, o, n) \
> diff --git a/arch/alpha/include/asm/xchg.h b/arch/alpha/include/asm/xchg.h
> index e2b59fac5257d..7adb80c6746ac 100644
> --- a/arch/alpha/include/asm/xchg.h
> +++ b/arch/alpha/include/asm/xchg.h
> @@ -12,10 +12,6 @@
> * Atomic exchange.
> * Since it can be used to implement critical sections
> * it must clobber "memory" (also for interrupts in UP).
> - *
> - * The leading and the trailing memory barriers guarantee that these
> - * operations are fully ordered.
> - *
> */
>
> static inline unsigned long
> @@ -23,7 +19,6 @@ ____xchg(_u8, volatile char *m, unsigned long val)
> {
> unsigned long ret, tmp, addr64;
>
> - smp_mb();
> __asm__ __volatile__(
> " andnot %4,7,%3\n"
> " insbl %1,%4,%1\n"
> @@ -38,7 +33,6 @@ ____xchg(_u8, volatile char *m, unsigned long val)
> ".previous"
> : "=&r" (ret), "=&r" (val), "=&r" (tmp), "=&r" (addr64)
> : "r" ((long)m), "1" (val) : "memory");
> - smp_mb();
>
> return ret;
> }
> @@ -48,7 +42,6 @@ ____xchg(_u16, volatile short *m, unsigned long val)
> {
> unsigned long ret, tmp, addr64;
>
> - smp_mb();
> __asm__ __volatile__(
> " andnot %4,7,%3\n"
> " inswl %1,%4,%1\n"
> @@ -63,7 +56,6 @@ ____xchg(_u16, volatile short *m, unsigned long val)
> ".previous"
> : "=&r" (ret), "=&r" (val), "=&r" (tmp), "=&r" (addr64)
> : "r" ((long)m), "1" (val) : "memory");
> - smp_mb();
>
> return ret;
> }
> @@ -73,7 +65,6 @@ ____xchg(_u32, volatile int *m, unsigned long val)
> {
> unsigned long dummy;
>
> - smp_mb();
> __asm__ __volatile__(
> "1: ldl_l %0,%4\n"
> " bis $31,%3,%1\n"
> @@ -84,7 +75,6 @@ ____xchg(_u32, volatile int *m, unsigned long val)
> ".previous"
> : "=&r" (val), "=&r" (dummy), "=m" (*m)
> : "rI" (val), "m" (*m) : "memory");
> - smp_mb();
>
> return val;
> }
> @@ -94,7 +84,6 @@ ____xchg(_u64, volatile long *m, unsigned long val)
> {
> unsigned long dummy;
>
> - smp_mb();
> __asm__ __volatile__(
> "1: ldq_l %0,%4\n"
> " bis $31,%3,%1\n"
> @@ -105,7 +94,6 @@ ____xchg(_u64, volatile long *m, unsigned long val)
> ".previous"
> : "=&r" (val), "=&r" (dummy), "=m" (*m)
> : "rI" (val), "m" (*m) : "memory");
> - smp_mb();
>
> return val;
> }
> @@ -135,13 +123,6 @@ ____xchg(, volatile void *ptr, unsigned long x, int size)
> * Atomic compare and exchange. Compare OLD with MEM, if identical,
> * store NEW in MEM. Return the initial value in MEM. Success is
> * indicated by comparing RETURN with OLD.
> - *
> - * The leading and the trailing memory barriers guarantee that these
> - * operations are fully ordered.
> - *
> - * The trailing memory barrier is placed in SMP unconditionally, in
> - * order to guarantee that dependency ordering is preserved when a
> - * dependency is headed by an unsuccessful operation.
> */
>
> static inline unsigned long
> @@ -149,7 +130,6 @@ ____cmpxchg(_u8, volatile char *m, unsigned char old, unsigned char new)
> {
> unsigned long prev, tmp, cmp, addr64;
>
> - smp_mb();
> __asm__ __volatile__(
> " andnot %5,7,%4\n"
> " insbl %1,%5,%1\n"
> @@ -167,7 +147,6 @@ ____cmpxchg(_u8, volatile char *m, unsigned char old, unsigned char new)
> ".previous"
> : "=&r" (prev), "=&r" (new), "=&r" (tmp), "=&r" (cmp), "=&r" (addr64)
> : "r" ((long)m), "Ir" (old), "1" (new) : "memory");
> - smp_mb();
>
> return prev;
> }
> @@ -177,7 +156,6 @@ ____cmpxchg(_u16, volatile short *m, unsigned short old, unsigned short new)
> {
> unsigned long prev, tmp, cmp, addr64;
>
> - smp_mb();
> __asm__ __volatile__(
> " andnot %5,7,%4\n"
> " inswl %1,%5,%1\n"
> @@ -195,7 +173,6 @@ ____cmpxchg(_u16, volatile short *m, unsigned short old, unsigned short new)
> ".previous"
> : "=&r" (prev), "=&r" (new), "=&r" (tmp), "=&r" (cmp), "=&r" (addr64)
> : "r" ((long)m), "Ir" (old), "1" (new) : "memory");
> - smp_mb();
>
> return prev;
> }
> @@ -205,7 +182,6 @@ ____cmpxchg(_u32, volatile int *m, int old, int new)
> {
> unsigned long prev, cmp;
>
> - smp_mb();
> __asm__ __volatile__(
> "1: ldl_l %0,%5\n"
> " cmpeq %0,%3,%1\n"
> @@ -219,7 +195,6 @@ ____cmpxchg(_u32, volatile int *m, int old, int new)
> ".previous"
> : "=&r"(prev), "=&r"(cmp), "=m"(*m)
> : "r"((long) old), "r"(new), "m"(*m) : "memory");
> - smp_mb();
>
> return prev;
> }
> @@ -229,7 +204,6 @@ ____cmpxchg(_u64, volatile long *m, unsigned long old, unsigned long new)
> {
> unsigned long prev, cmp;
>
> - smp_mb();
> __asm__ __volatile__(
> "1: ldq_l %0,%5\n"
> " cmpeq %0,%3,%1\n"
> @@ -243,7 +217,6 @@ ____cmpxchg(_u64, volatile long *m, unsigned long old, unsigned long new)
> ".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] 5+ messages in thread* Re: [PATCH] locking/xchg/alpha: Remove memory barriers from the _local() variants
2018-02-27 20:08 ` Andrea Parri
@ 2018-02-28 10:58 ` Will Deacon
2018-02-28 11:26 ` Andrea Parri
0 siblings, 1 reply; 5+ messages in thread
From: Will Deacon @ 2018-02-28 10:58 UTC (permalink / raw)
To: Andrea Parri
Cc: Ingo Molnar, Peter Zijlstra, linux-kernel, Paul E . McKenney,
Alan Stern, Andrew Morton, Ivan Kokshaysky, Linus Torvalds,
Matt Turner, Richard Henderson, Thomas Gleixner, linux-alpha
On Tue, Feb 27, 2018 at 09:08:31PM +0100, Andrea Parri wrote:
> [+ Will]
>
> I'm not sure how this happened; Will, you at least figure as Reported-by: ;-)
Thanks, this looks better to me. Have you build an Alpha kernel to check
that the various cmpxchg variants are producing the expected asm?
Will
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] locking/xchg/alpha: Remove memory barriers from the _local() variants
2018-02-28 10:58 ` Will Deacon
@ 2018-02-28 11:26 ` Andrea Parri
0 siblings, 0 replies; 5+ messages in thread
From: Andrea Parri @ 2018-02-28 11:26 UTC (permalink / raw)
To: Will Deacon
Cc: Ingo Molnar, Peter Zijlstra, linux-kernel, Paul E . McKenney,
Alan Stern, Andrew Morton, Ivan Kokshaysky, Linus Torvalds,
Matt Turner, Richard Henderson, Thomas Gleixner, linux-alpha
On Wed, Feb 28, 2018 at 10:58:11AM +0000, Will Deacon wrote:
> On Tue, Feb 27, 2018 at 09:08:31PM +0100, Andrea Parri wrote:
> > [+ Will]
> >
> > I'm not sure how this happened; Will, you at least figure as Reported-by: ;-)
>
> Thanks, this looks better to me. Have you build an Alpha kernel to check
> that the various cmpxchg variants are producing the expected asm?
Indeed. Compile tested (only).
Andrea
>
> Will
^ permalink raw reply [flat|nested] 5+ messages in thread
* [tip:locking/core] locking/xchg/alpha: Remove superfluous memory barriers from the _local() variants
2018-02-27 4:00 [PATCH] locking/xchg/alpha: Remove memory barriers from the _local() variants Andrea Parri
2018-02-27 20:08 ` Andrea Parri
@ 2018-03-12 12:17 ` tip-bot for Andrea Parri
1 sibling, 0 replies; 5+ messages in thread
From: tip-bot for Andrea Parri @ 2018-03-12 12:17 UTC (permalink / raw)
To: linux-tip-commits
Cc: mingo, ink, hpa, stern, linux-kernel, rth, torvalds,
parri.andrea, mattst88, tglx, will.deacon, paulmck, peterz, akpm
Commit-ID: fbfcd0199170984bd3c2812e49ed0fe7b226959a
Gitweb: https://git.kernel.org/tip/fbfcd0199170984bd3c2812e49ed0fe7b226959a
Author: Andrea Parri <parri.andrea@gmail.com>
AuthorDate: Tue, 27 Feb 2018 05:00:58 +0100
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 12 Mar 2018 10:59:03 +0100
locking/xchg/alpha: Remove superfluous memory barriers from the _local() variants
The following two commits:
79d442461df74 ("locking/xchg/alpha: Clean up barrier usage by using smp_mb() in place of __ASM__MB")
472e8c55cf662 ("locking/xchg/alpha: Fix xchg() and cmpxchg() memory ordering bugs")
... ended up adding unnecessary barriers to the _local() variants on Alpha,
which the previous code took care to avoid.
Fix them by adding the smp_mb() into the cmpxchg() macro rather than into the
____cmpxchg() variants.
Reported-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrea Parri <parri.andrea@gmail.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: Paul E. McKenney <paulmck@linux.vnet.ibm.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
Fixes: 472e8c55cf662 ("locking/xchg/alpha: Fix xchg() and cmpxchg() memory ordering bugs")
Fixes: 79d442461df74 ("locking/xchg/alpha: Clean up barrier usage by using smp_mb() in place of __ASM__MB")
Link: http://lkml.kernel.org/r/1519704058-13430-1-git-send-email-parri.andrea@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/alpha/include/asm/cmpxchg.h | 20 ++++++++++++++++----
arch/alpha/include/asm/xchg.h | 27 ---------------------------
2 files changed, 16 insertions(+), 31 deletions(-)
diff --git a/arch/alpha/include/asm/cmpxchg.h b/arch/alpha/include/asm/cmpxchg.h
index 8a2b331e43fe..6c7c39452471 100644
--- a/arch/alpha/include/asm/cmpxchg.h
+++ b/arch/alpha/include/asm/cmpxchg.h
@@ -38,19 +38,31 @@
#define ____cmpxchg(type, args...) __cmpxchg ##type(args)
#include <asm/xchg.h>
+/*
+ * The leading and the trailing memory barriers guarantee that these
+ * operations are fully ordered.
+ */
#define xchg(ptr, x) \
({ \
+ __typeof__(*(ptr)) __ret; \
__typeof__(*(ptr)) _x_ = (x); \
- (__typeof__(*(ptr))) __xchg((ptr), (unsigned long)_x_, \
- sizeof(*(ptr))); \
+ smp_mb(); \
+ __ret = (__typeof__(*(ptr))) \
+ __xchg((ptr), (unsigned long)_x_, sizeof(*(ptr))); \
+ smp_mb(); \
+ __ret; \
})
#define cmpxchg(ptr, o, n) \
({ \
+ __typeof__(*(ptr)) __ret; \
__typeof__(*(ptr)) _o_ = (o); \
__typeof__(*(ptr)) _n_ = (n); \
- (__typeof__(*(ptr))) __cmpxchg((ptr), (unsigned long)_o_, \
- (unsigned long)_n_, sizeof(*(ptr)));\
+ smp_mb(); \
+ __ret = (__typeof__(*(ptr))) __cmpxchg((ptr), \
+ (unsigned long)_o_, (unsigned long)_n_, sizeof(*(ptr)));\
+ smp_mb(); \
+ __ret; \
})
#define cmpxchg64(ptr, o, n) \
diff --git a/arch/alpha/include/asm/xchg.h b/arch/alpha/include/asm/xchg.h
index e2b59fac5257..7adb80c6746a 100644
--- a/arch/alpha/include/asm/xchg.h
+++ b/arch/alpha/include/asm/xchg.h
@@ -12,10 +12,6 @@
* Atomic exchange.
* Since it can be used to implement critical sections
* it must clobber "memory" (also for interrupts in UP).
- *
- * The leading and the trailing memory barriers guarantee that these
- * operations are fully ordered.
- *
*/
static inline unsigned long
@@ -23,7 +19,6 @@ ____xchg(_u8, volatile char *m, unsigned long val)
{
unsigned long ret, tmp, addr64;
- smp_mb();
__asm__ __volatile__(
" andnot %4,7,%3\n"
" insbl %1,%4,%1\n"
@@ -38,7 +33,6 @@ ____xchg(_u8, volatile char *m, unsigned long val)
".previous"
: "=&r" (ret), "=&r" (val), "=&r" (tmp), "=&r" (addr64)
: "r" ((long)m), "1" (val) : "memory");
- smp_mb();
return ret;
}
@@ -48,7 +42,6 @@ ____xchg(_u16, volatile short *m, unsigned long val)
{
unsigned long ret, tmp, addr64;
- smp_mb();
__asm__ __volatile__(
" andnot %4,7,%3\n"
" inswl %1,%4,%1\n"
@@ -63,7 +56,6 @@ ____xchg(_u16, volatile short *m, unsigned long val)
".previous"
: "=&r" (ret), "=&r" (val), "=&r" (tmp), "=&r" (addr64)
: "r" ((long)m), "1" (val) : "memory");
- smp_mb();
return ret;
}
@@ -73,7 +65,6 @@ ____xchg(_u32, volatile int *m, unsigned long val)
{
unsigned long dummy;
- smp_mb();
__asm__ __volatile__(
"1: ldl_l %0,%4\n"
" bis $31,%3,%1\n"
@@ -84,7 +75,6 @@ ____xchg(_u32, volatile int *m, unsigned long val)
".previous"
: "=&r" (val), "=&r" (dummy), "=m" (*m)
: "rI" (val), "m" (*m) : "memory");
- smp_mb();
return val;
}
@@ -94,7 +84,6 @@ ____xchg(_u64, volatile long *m, unsigned long val)
{
unsigned long dummy;
- smp_mb();
__asm__ __volatile__(
"1: ldq_l %0,%4\n"
" bis $31,%3,%1\n"
@@ -105,7 +94,6 @@ ____xchg(_u64, volatile long *m, unsigned long val)
".previous"
: "=&r" (val), "=&r" (dummy), "=m" (*m)
: "rI" (val), "m" (*m) : "memory");
- smp_mb();
return val;
}
@@ -135,13 +123,6 @@ ____xchg(, volatile void *ptr, unsigned long x, int size)
* Atomic compare and exchange. Compare OLD with MEM, if identical,
* store NEW in MEM. Return the initial value in MEM. Success is
* indicated by comparing RETURN with OLD.
- *
- * The leading and the trailing memory barriers guarantee that these
- * operations are fully ordered.
- *
- * The trailing memory barrier is placed in SMP unconditionally, in
- * order to guarantee that dependency ordering is preserved when a
- * dependency is headed by an unsuccessful operation.
*/
static inline unsigned long
@@ -149,7 +130,6 @@ ____cmpxchg(_u8, volatile char *m, unsigned char old, unsigned char new)
{
unsigned long prev, tmp, cmp, addr64;
- smp_mb();
__asm__ __volatile__(
" andnot %5,7,%4\n"
" insbl %1,%5,%1\n"
@@ -167,7 +147,6 @@ ____cmpxchg(_u8, volatile char *m, unsigned char old, unsigned char new)
".previous"
: "=&r" (prev), "=&r" (new), "=&r" (tmp), "=&r" (cmp), "=&r" (addr64)
: "r" ((long)m), "Ir" (old), "1" (new) : "memory");
- smp_mb();
return prev;
}
@@ -177,7 +156,6 @@ ____cmpxchg(_u16, volatile short *m, unsigned short old, unsigned short new)
{
unsigned long prev, tmp, cmp, addr64;
- smp_mb();
__asm__ __volatile__(
" andnot %5,7,%4\n"
" inswl %1,%5,%1\n"
@@ -195,7 +173,6 @@ ____cmpxchg(_u16, volatile short *m, unsigned short old, unsigned short new)
".previous"
: "=&r" (prev), "=&r" (new), "=&r" (tmp), "=&r" (cmp), "=&r" (addr64)
: "r" ((long)m), "Ir" (old), "1" (new) : "memory");
- smp_mb();
return prev;
}
@@ -205,7 +182,6 @@ ____cmpxchg(_u32, volatile int *m, int old, int new)
{
unsigned long prev, cmp;
- smp_mb();
__asm__ __volatile__(
"1: ldl_l %0,%5\n"
" cmpeq %0,%3,%1\n"
@@ -219,7 +195,6 @@ ____cmpxchg(_u32, volatile int *m, int old, int new)
".previous"
: "=&r"(prev), "=&r"(cmp), "=m"(*m)
: "r"((long) old), "r"(new), "m"(*m) : "memory");
- smp_mb();
return prev;
}
@@ -229,7 +204,6 @@ ____cmpxchg(_u64, volatile long *m, unsigned long old, unsigned long new)
{
unsigned long prev, cmp;
- smp_mb();
__asm__ __volatile__(
"1: ldq_l %0,%5\n"
" cmpeq %0,%3,%1\n"
@@ -243,7 +217,6 @@ ____cmpxchg(_u64, volatile long *m, unsigned long old, unsigned long new)
".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] 5+ messages in thread
end of thread, other threads:[~2018-03-12 12:17 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-02-27 4:00 [PATCH] locking/xchg/alpha: Remove memory barriers from the _local() variants Andrea Parri
2018-02-27 20:08 ` Andrea Parri
2018-02-28 10:58 ` Will Deacon
2018-02-28 11:26 ` Andrea Parri
2018-03-12 12:17 ` [tip:locking/core] locking/xchg/alpha: Remove superfluous " tip-bot for Andrea Parri
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