Commit 9a0b26e6 authored by Andi Kleen's avatar Andi Kleen Committed by Andi Kleen
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[PATCH] Clean up read write lock assembly



- Move the slow path fallbacks to their own assembly files
This makes them much easier to read and is needed for the next change.
- Add CFI annotations for unwinding (XXX need review)
- Remove constant case which can never happen with out of line spinlocks
- Use patchable LOCK prefixes
- Don't use lock sections anymore for inline code because they can't
be expressed by the unwinder (this adds one taken jump to the lock
fast path)

Cc: jbeulich@novell.com
Signed-off-by: default avatarAndi Kleen <ak@suse.de>
parent b4062b16
......@@ -9,4 +9,4 @@ obj-y := io.o iomap_copy.o
lib-y := csum-partial.o csum-copy.o csum-wrappers.o delay.o \
usercopy.o getuser.o putuser.o \
thunk.o clear_page.o copy_page.o bitstr.o bitops.o
lib-y += memcpy.o memmove.o memset.o copy_user.o
lib-y += memcpy.o memmove.o memset.o copy_user.o rwlock.o
/* Slow paths of read/write spinlocks. */
#include <linux/linkage.h>
#include <asm/rwlock.h>
#include <asm/alternative-asm.i>
#include <asm/dwarf2.h>
/* rdi: pointer to rwlock_t */
ENTRY(__write_lock_failed)
CFI_STARTPROC
LOCK_PREFIX
addl $RW_LOCK_BIAS,(%rdi)
1: rep
nop
cmpl $RW_LOCK_BIAS,(%rdi)
jne 1b
LOCK_PREFIX
subl $RW_LOCK_BIAS,(%rdi)
jnz __write_lock_failed
ret
CFI_ENDPROC
END(__write_lock_failed)
/* rdi: pointer to rwlock_t */
ENTRY(__read_lock_failed)
CFI_STARTPROC
LOCK_PREFIX
incl (%rdi)
1: rep
nop
cmpl $1,(%rdi)
js 1b
LOCK_PREFIX
decl (%rdi)
js __read_lock_failed
ret
CFI_ENDPROC
END(__read_lock_failed)
......@@ -67,33 +67,3 @@ restore_norax:
RESTORE_ARGS 1
ret
CFI_ENDPROC
#ifdef CONFIG_SMP
/* Support for read/write spinlocks. */
.text
/* rax: pointer to rwlock_t */
ENTRY(__write_lock_failed)
lock
addl $RW_LOCK_BIAS,(%rax)
1: rep
nop
cmpl $RW_LOCK_BIAS,(%rax)
jne 1b
lock
subl $RW_LOCK_BIAS,(%rax)
jnz __write_lock_failed
ret
/* rax: pointer to rwlock_t */
ENTRY(__read_lock_failed)
lock
incl (%rax)
1: rep
nop
cmpl $1,(%rax)
js 1b
lock
decl (%rax)
js __read_lock_failed
ret
#endif
......@@ -18,69 +18,21 @@
#ifndef _ASM_X86_64_RWLOCK_H
#define _ASM_X86_64_RWLOCK_H
#include <linux/stringify.h>
#define RW_LOCK_BIAS 0x01000000
#define RW_LOCK_BIAS_STR "0x01000000"
#define RW_LOCK_BIAS_STR "0x01000000"
#define __build_read_lock_ptr(rw, helper) \
#define __build_read_lock(rw) \
asm volatile(LOCK_PREFIX "subl $1,(%0)\n\t" \
"js 2f\n" \
"1:\n" \
LOCK_SECTION_START("") \
"2:\tcall " helper "\n\t" \
"jmp 1b\n" \
LOCK_SECTION_END \
::"a" (rw) : "memory")
#define __build_read_lock_const(rw, helper) \
asm volatile(LOCK_PREFIX "subl $1,%0\n\t" \
"js 2f\n" \
"jns 1f\n" \
"call __read_lock_failed\n" \
"1:\n" \
LOCK_SECTION_START("") \
"2:\tpushq %%rax\n\t" \
"leaq %0,%%rax\n\t" \
"call " helper "\n\t" \
"popq %%rax\n\t" \
"jmp 1b\n" \
LOCK_SECTION_END \
:"=m" (*((volatile int *)rw))::"memory")
#define __build_read_lock(rw, helper) do { \
if (__builtin_constant_p(rw)) \
__build_read_lock_const(rw, helper); \
else \
__build_read_lock_ptr(rw, helper); \
} while (0)
::"D" (rw), "i" (RW_LOCK_BIAS) : "memory")
#define __build_write_lock_ptr(rw, helper) \
asm volatile(LOCK_PREFIX "subl $" RW_LOCK_BIAS_STR ",(%0)\n\t" \
"jnz 2f\n" \
#define __build_write_lock(rw) \
asm volatile(LOCK_PREFIX "subl %1,(%0)\n\t" \
"jz 1f\n" \
"\tcall __write_lock_failed\n\t" \
"1:\n" \
LOCK_SECTION_START("") \
"2:\tcall " helper "\n\t" \
"jmp 1b\n" \
LOCK_SECTION_END \
::"a" (rw) : "memory")
#define __build_write_lock_const(rw, helper) \
asm volatile(LOCK_PREFIX "subl $" RW_LOCK_BIAS_STR ",%0\n\t" \
"jnz 2f\n" \
"1:\n" \
LOCK_SECTION_START("") \
"2:\tpushq %%rax\n\t" \
"leaq %0,%%rax\n\t" \
"call " helper "\n\t" \
"popq %%rax\n\t" \
"jmp 1b\n" \
LOCK_SECTION_END \
:"=m" (*((volatile long *)rw))::"memory")
#define __build_write_lock(rw, helper) do { \
if (__builtin_constant_p(rw)) \
__build_write_lock_const(rw, helper); \
else \
__build_write_lock_ptr(rw, helper); \
} while (0)
::"D" (rw), "i" (RW_LOCK_BIAS) : "memory")
#endif
......@@ -79,13 +79,6 @@ static inline void __raw_spin_unlock(raw_spinlock_t *lock)
*
* On x86, we implement read-write locks as a 32-bit counter
* with the high bit (sign) being the "contended" bit.
*
* The inline assembly is non-obvious. Think about it.
*
* Changed to use the same technique as rw semaphores. See
* semaphore.h for details. -ben
*
* the helpers are in arch/i386/kernel/semaphore.c
*/
#define __raw_read_can_lock(x) ((int)(x)->lock > 0)
......@@ -93,12 +86,12 @@ static inline void __raw_spin_unlock(raw_spinlock_t *lock)
static inline void __raw_read_lock(raw_rwlock_t *rw)
{
__build_read_lock(rw, "__read_lock_failed");
__build_read_lock(rw);
}
static inline void __raw_write_lock(raw_rwlock_t *rw)
{
__build_write_lock(rw, "__write_lock_failed");
__build_write_lock(rw);
}
static inline int __raw_read_trylock(raw_rwlock_t *lock)
......
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