On 3/27/11 4:57 AM, Christoph Lameter wrote:
But then the same fix must also be used in the asm code or the fallback
(turns out that the fallback is always used in kmem_cache_init since
the instruction patching comes later).
Patch boots fine both in UP and SMP mode
Subject: percpu: Omit segment prefix in the UP case for cmpxchg_double
Omit the segment prefix in the UP case. GS is not used then
and we will generate segfaults if cmpxchg16b is used otherwise.
Signed-off-by: Linus Torvalds<torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Christoph Lameter<cl@xxxxxxxxx>
arch/x86/include/asm/percpu.h | 10 ++++++----
1 files changed, 6 insertions(+), 4 deletions(-)
Index: linux-2.6/arch/x86/include/asm/percpu.h
===================================================================
--- linux-2.6.orig/arch/x86/include/asm/percpu.h 2011-03-26 20:43:03.994089001 -0500
+++ linux-2.6/arch/x86/include/asm/percpu.h 2011-03-26 20:43:22.414089004 -0500
@@ -45,7 +45,7 @@
#include<linux/stringify.h>
#ifdef CONFIG_SMP
-#define __percpu_arg(x) "%%"__stringify(__percpu_seg)":%P" #x
+#define __percpu_prefix "%%"__stringify(__percpu_seg)":"
#define __my_cpu_offset percpu_read(this_cpu_off)
/*
@@ -62,9 +62,11 @@
(typeof(*(ptr)) __kernel __force *)tcp_ptr__; \
})
#else
-#define __percpu_arg(x) "%P" #x
+#define __percpu_prefix ""
#endif
+#define __percpu_arg(x) __percpu_prefix "%P" #x
+
/*
* Initialized pointers to per-cpu variables needed for the boot
* processor need to use these macros to get the proper address
@@ -516,11 +518,11 @@
typeof(o2) __n2 = n2; \
typeof(o2) __dummy; \
alternative_io("call this_cpu_cmpxchg16b_emu\n\t" P6_NOP4, \
- "cmpxchg16b %%gs:(%%rsi)\n\tsetz %0\n\t", \
+ "cmpxchg16b " __percpu_prefix "(%%rsi)\n\tsetz %0\n\t", \
X86_FEATURE_CX16, \
ASM_OUTPUT2("=a"(__ret), "=d"(__dummy)), \
"S" (&pcp1), "b"(__n1), "c"(__n2), \
- "a"(__o1), "d"(__o2)); \
+ "a"(__o1), "d"(__o2) : "memory"); \
__ret; \
})
Index: linux-2.6/arch/x86/lib/cmpxchg16b_emu.S
===================================================================
--- linux-2.6.orig/arch/x86/lib/cmpxchg16b_emu.S 2011-03-26 20:43:57.384089004 -0500
+++ linux-2.6/arch/x86/lib/cmpxchg16b_emu.S 2011-03-26 20:48:42.684088999 -0500
@@ -10,6 +10,12 @@
#include<asm/frame.h>
#include<asm/dwarf2.h>
+#ifdef CONFIG_SMP
+#define SEG_PREFIX %gs:
+#else
+#define SEG_PREFIX
+#endif
+
.text
/*
@@ -37,13 +43,13 @@
pushf
cli
- cmpq %gs:(%rsi), %rax
+ cmpq SEG_PREFIX(%rsi), %rax
jne not_same
- cmpq %gs:8(%rsi), %rdx
+ cmpq SEG_PREFIX 8(%rsi), %rdx
jne not_same
- movq %rbx, %gs:(%rsi)
- movq %rcx, %gs:8(%rsi)
+ movq %rbx, SEG_PREFIX(%rsi)
+ movq %rcx, SEG_PREFIX 8(%rsi)
popf
mov $1, %al
Tejun, does this look good to you as well? I think it should go through
the percpu tree. It's needed to fix a boot crash with lockless SLUB
fastpaths enabled.
Pekka
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