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SubjectRe: [tip:x86/urgent] x86: Add memory modify constraints to xchg() and cmpxchg()
On Mon, 02 Aug 2010, Jeremy Fitzhardinge wrote:

>> Commit-ID: 113fc5a6e8c2288619ff7e8187a6f556b7e0d372
>> Gitweb: http://git.kernel.org/tip/113fc5a6e8c2288619ff7e8187a6f556b7e0d372
>> Author: H. Peter Anvin<hpa@zytor.com>
>> AuthorDate: Tue, 27 Jul 2010 17:01:49 -0700
>> Committer: H. Peter Anvin<hpa@zytor.com>
>> CommitDate: Tue, 27 Jul 2010 17:14:02 -0700
>>
>> x86: Add memory modify constraints to xchg() and cmpxchg()
>
> Here's the 2.6.32 version for stable.

Thanks a lot everyone. This patch resolves the issue for me on top
of 2.6.32.17.

(I had some whitespace issue with applying the patch, so I've attached
the cleaned up version in case it wasn't just me.)

Cheers,
Peter
--
| .''`. ** Debian GNU/Linux **
Peter Palfrader | : :' : The universal
http://www.palfrader.org/ | `. `' Operating System
| `- http://www.debian.org/From f6fd342ddae3f7edecd0254e5c4e6795d4fba4a9 Mon Sep 17 00:00:00 2001
From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Date: Tue, 27 Jul 2010 23:03:58 -0700
Subject: [PATCH] x86: Add memory modify constraints to xchg() and cmpxchg()

xchg() and cmpxchg() modify their memory operands, not merely read
them. For some versions of gcc the "memory" clobber has apparently
dealt with the situation, but not for all.

Also adds the missing 8-byte case for __sync_cmpxchg().

Based on HPA's patch.

Signed-off-by: Jeremy Fitzhardinge<jeremy.fitzhardinge@citrix.com>
Cc: "H. Peter Anvin"<hpa@zytor.com>
Cc: Stable Kernel<stable@kernel.org>
---
arch/x86/include/asm/cmpxchg_32.h | 86 +++++++++++++++++------------------
arch/x86/include/asm/cmpxchg_64.h | 88 ++++++++++++++++++++-----------------
2 files changed, 89 insertions(+), 85 deletions(-)
diff --git a/arch/x86/include/asm/cmpxchg_32.h b/arch/x86/include/asm/cmpxchg_32.h
index ee1931b..5af5051 100644
--- a/arch/x86/include/asm/cmpxchg_32.h
+++ b/arch/x86/include/asm/cmpxchg_32.h
@@ -34,12 +34,12 @@ static inline void __set_64bit(unsigned long long *ptr,
unsigned int low, unsigned int high)
{
asm volatile("\n1:\t"
- "movl (%0), %%eax\n\t"
- "movl 4(%0), %%edx\n\t"
- LOCK_PREFIX "cmpxchg8b (%0)\n\t"
+ "movl (%1), %%eax\n\t"
+ "movl 4(%1), %%edx\n\t"
+ LOCK_PREFIX "cmpxchg8b %0\n\t"
"jnz 1b"
- : /* no outputs */
- : "D"(ptr),
+ : "=m"(*ptr)
+ : "D" (ptr),
"b"(low),
"c"(high)
: "ax", "dx", "memory");
@@ -82,20 +82,20 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr,
switch (size) {
case 1:
asm volatile("xchgb %b0,%1"
- : "=q" (x)
- : "m" (*__xg(ptr)), "0" (x)
+ : "=q" (x), "+m" (*__xg(ptr))
+ : "0" (x)
: "memory");
break;
case 2:
asm volatile("xchgw %w0,%1"
- : "=r" (x)
- : "m" (*__xg(ptr)), "0" (x)
+ : "=r" (x), "+m" (*__xg(ptr))
+ : "0" (x)
: "memory");
break;
case 4:
asm volatile("xchgl %0,%1"
- : "=r" (x)
- : "m" (*__xg(ptr)), "0" (x)
+ : "=r" (x), "+m" (*__xg(ptr))
+ : "0" (x)
: "memory");
break;
}
@@ -139,21 +139,21 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
unsigned long prev;
switch (size) {
case 1:
- asm volatile(LOCK_PREFIX "cmpxchgb %b1,%2"
- : "=a"(prev)
- : "q"(new), "m"(*__xg(ptr)), "0"(old)
+ asm volatile(LOCK_PREFIX "cmpxchgb %b2,%1"
+ : "=a"(prev), "+m"(*__xg(ptr))
+ : "q"(new), "0"(old)
: "memory");
return prev;
case 2:
- asm volatile(LOCK_PREFIX "cmpxchgw %w1,%2"
- : "=a"(prev)
- : "r"(new), "m"(*__xg(ptr)), "0"(old)
+ asm volatile(LOCK_PREFIX "cmpxchgw %w2,%1"
+ : "=a"(prev), "+m"(*__xg(ptr))
+ : "r"(new), "0"(old)
: "memory");
return prev;
case 4:
- asm volatile(LOCK_PREFIX "cmpxchgl %1,%2"
- : "=a"(prev)
- : "r"(new), "m"(*__xg(ptr)), "0"(old)
+ asm volatile(LOCK_PREFIX "cmpxchgl %2,%1"
+ : "=a"(prev), "+m"(*__xg(ptr))
+ : "r"(new), "0"(old)
: "memory");
return prev;
}
@@ -172,21 +172,21 @@ static inline unsigned long __sync_cmpxchg(volatile void *ptr,
unsigned long prev;
switch (size) {
case 1:
- asm volatile("lock; cmpxchgb %b1,%2"
- : "=a"(prev)
- : "q"(new), "m"(*__xg(ptr)), "0"(old)
+ asm volatile("lock; cmpxchgb %b2,%1"
+ : "=a"(prev), "+m"(*__xg(ptr))
+ : "q"(new), "0"(old)
: "memory");
return prev;
case 2:
- asm volatile("lock; cmpxchgw %w1,%2"
- : "=a"(prev)
- : "r"(new), "m"(*__xg(ptr)), "0"(old)
+ asm volatile("lock; cmpxchgw %w2,%1"
+ : "=a"(prev), "+m"(*__xg(ptr))
+ : "r"(new), "0"(old)
: "memory");
return prev;
case 4:
- asm volatile("lock; cmpxchgl %1,%2"
- : "=a"(prev)
- : "r"(new), "m"(*__xg(ptr)), "0"(old)
+ asm volatile("lock; cmpxchgl %2,%1"
+ : "=a"(prev), "+m"(*__xg(ptr))
+ : "r"(new), "0"(old)
: "memory");
return prev;
}
@@ -200,21 +200,21 @@ static inline unsigned long __cmpxchg_local(volatile void *ptr,
unsigned long prev;
switch (size) {
case 1:
- asm volatile("cmpxchgb %b1,%2"
- : "=a"(prev)
- : "q"(new), "m"(*__xg(ptr)), "0"(old)
+ asm volatile("cmpxchgb %b2,%1"
+ : "=a"(prev), "+m"(*__xg(ptr))
+ : "q"(new), "0"(old)
: "memory");
return prev;
case 2:
- asm volatile("cmpxchgw %w1,%2"
- : "=a"(prev)
- : "r"(new), "m"(*__xg(ptr)), "0"(old)
+ asm volatile("cmpxchgw %w2,%1"
+ : "=a"(prev), "+m"(*__xg(ptr))
+ : "r"(new), "0"(old)
: "memory");
return prev;
case 4:
- asm volatile("cmpxchgl %1,%2"
- : "=a"(prev)
- : "r"(new), "m"(*__xg(ptr)), "0"(old)
+ asm volatile("cmpxchgl %2,%1"
+ : "=a"(prev), "+m"(*__xg(ptr))
+ : "r"(new), "0"(old)
: "memory");
return prev;
}
@@ -226,11 +226,10 @@ static inline unsigned long long __cmpxchg64(volatile void *ptr,
unsigned long long new)
{
unsigned long long prev;
- asm volatile(LOCK_PREFIX "cmpxchg8b %3"
- : "=A"(prev)
+ asm volatile(LOCK_PREFIX "cmpxchg8b %1"
+ : "=A"(prev), "+m" (*__xg(ptr))
: "b"((unsigned long)new),
"c"((unsigned long)(new >> 32)),
- "m"(*__xg(ptr)),
"0"(old)
: "memory");
return prev;
@@ -241,11 +240,10 @@ static inline unsigned long long __cmpxchg64_local(volatile void *ptr,
unsigned long long new)
{
unsigned long long prev;
- asm volatile("cmpxchg8b %3"
- : "=A"(prev)
+ asm volatile("cmpxchg8b %1"
+ : "=A"(prev), "+m"(*__xg(ptr))
: "b"((unsigned long)new),
"c"((unsigned long)(new >> 32)),
- "m"(*__xg(ptr)),
"0"(old)
: "memory");
return prev;
diff --git a/arch/x86/include/asm/cmpxchg_64.h b/arch/x86/include/asm/cmpxchg_64.h
index 52de72e..1871cb0 100644
--- a/arch/x86/include/asm/cmpxchg_64.h
+++ b/arch/x86/include/asm/cmpxchg_64.h
@@ -26,26 +26,26 @@ static inline unsigned long __xchg(unsigned long x, volatile void *ptr,
switch (size) {
case 1:
asm volatile("xchgb %b0,%1"
- : "=q" (x)
- : "m" (*__xg(ptr)), "0" (x)
+ : "=q" (x), "+m" (*__xg(ptr))
+ : "0" (x)
: "memory");
break;
case 2:
asm volatile("xchgw %w0,%1"
- : "=r" (x)
- : "m" (*__xg(ptr)), "0" (x)
+ : "=r" (x), "+m" (*__xg(ptr))
+ : "0" (x)
: "memory");
break;
case 4:
asm volatile("xchgl %k0,%1"
- : "=r" (x)
- : "m" (*__xg(ptr)), "0" (x)
+ : "=r" (x), "+m" (*__xg(ptr))
+ : "0" (x)
: "memory");
break;
case 8:
asm volatile("xchgq %0,%1"
- : "=r" (x)
- : "m" (*__xg(ptr)), "0" (x)
+ : "=r" (x), "+m" (*__xg(ptr))
+ : "0" (x)
: "memory");
break;
}
@@ -66,27 +66,27 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
unsigned long prev;
switch (size) {
case 1:
- asm volatile(LOCK_PREFIX "cmpxchgb %b1,%2"
- : "=a"(prev)
- : "q"(new), "m"(*__xg(ptr)), "0"(old)
+ asm volatile(LOCK_PREFIX "cmpxchgb %b2,%1"
+ : "=a"(prev), "+m"(*__xg(ptr))
+ : "q"(new), "0"(old)
: "memory");
return prev;
case 2:
- asm volatile(LOCK_PREFIX "cmpxchgw %w1,%2"
- : "=a"(prev)
- : "r"(new), "m"(*__xg(ptr)), "0"(old)
+ asm volatile(LOCK_PREFIX "cmpxchgw %w2,%1"
+ : "=a"(prev), "+m"(*__xg(ptr))
+ : "r"(new), "0"(old)
: "memory");
return prev;
case 4:
- asm volatile(LOCK_PREFIX "cmpxchgl %k1,%2"
- : "=a"(prev)
- : "r"(new), "m"(*__xg(ptr)), "0"(old)
+ asm volatile(LOCK_PREFIX "cmpxchgl %k2,%1"
+ : "=a"(prev), "+m"(*__xg(ptr))
+ : "r"(new), "0"(old)
: "memory");
return prev;
case 8:
- asm volatile(LOCK_PREFIX "cmpxchgq %1,%2"
- : "=a"(prev)
- : "r"(new), "m"(*__xg(ptr)), "0"(old)
+ asm volatile(LOCK_PREFIX "cmpxchgq %2,%1"
+ : "=a"(prev), "+m"(*__xg(ptr))
+ : "r"(new), "0"(old)
: "memory");
return prev;
}
@@ -105,21 +105,27 @@ static inline unsigned long __sync_cmpxchg(volatile void *ptr,
unsigned long prev;
switch (size) {
case 1:
- asm volatile("lock; cmpxchgb %b1,%2"
- : "=a"(prev)
- : "q"(new), "m"(*__xg(ptr)), "0"(old)
+ asm volatile("lock; cmpxchgb %b2,%1"
+ : "=a"(prev), "+m"(*__xg(ptr))
+ : "q"(new), "0"(old)
: "memory");
return prev;
case 2:
- asm volatile("lock; cmpxchgw %w1,%2"
- : "=a"(prev)
- : "r"(new), "m"(*__xg(ptr)), "0"(old)
+ asm volatile("lock; cmpxchgw %w2,%1"
+ : "=a"(prev), "+m"(*__xg(ptr))
+ : "r"(new), "0"(old)
: "memory");
return prev;
case 4:
- asm volatile("lock; cmpxchgl %1,%2"
- : "=a"(prev)
- : "r"(new), "m"(*__xg(ptr)), "0"(old)
+ asm volatile("lock; cmpxchgl %k2,%1"
+ : "=a"(prev), "+m"(*__xg(ptr))
+ : "r"(new), "0"(old)
+ : "memory");
+ return prev;
+ case 8:
+ asm volatile("lock; cmpxchgq %2,%1"
+ : "=a"(prev), "+m"(*__xg(ptr))
+ : "r"(new), "0"(old)
: "memory");
return prev;
}
@@ -133,27 +139,27 @@ static inline unsigned long __cmpxchg_local(volatile void *ptr,
unsigned long prev;
switch (size) {
case 1:
- asm volatile("cmpxchgb %b1,%2"
- : "=a"(prev)
- : "q"(new), "m"(*__xg(ptr)), "0"(old)
+ asm volatile("cmpxchgb %b2,%1"
+ : "=a"(prev), "+m"(*__xg(ptr))
+ : "q"(new), "0"(old)
: "memory");
return prev;
case 2:
- asm volatile("cmpxchgw %w1,%2"
- : "=a"(prev)
- : "r"(new), "m"(*__xg(ptr)), "0"(old)
+ asm volatile("cmpxchgw %w2,%1"
+ : "=a"(prev), "+m"(*__xg(ptr))
+ : "r"(new), "0"(old)
: "memory");
return prev;
case 4:
- asm volatile("cmpxchgl %k1,%2"
- : "=a"(prev)
- : "r"(new), "m"(*__xg(ptr)), "0"(old)
+ asm volatile("cmpxchgl %k2,%1"
+ : "=a"(prev), "+m"(*__xg(ptr))
+ : "r"(new), "0"(old)
: "memory");
return prev;
case 8:
- asm volatile("cmpxchgq %1,%2"
- : "=a"(prev)
- : "r"(new), "m"(*__xg(ptr)), "0"(old)
+ asm volatile("cmpxchgq %2,%1"
+ : "=a"(prev), "+m"(*__xg(ptr))
+ : "r"(new), "0"(old)
: "memory");
return prev;
}
--
1.5.6.5
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