[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: Andi Kleen <ak@suse.de>

diff --git a/arch/x86_64/lib/Makefile b/arch/x86_64/lib/Makefile
index ccef6ae..b78d417 100644 (file)
--- a/arch/x86_64/lib/Makefile
+++ b/arch/x86_64/lib/Makefile
@@ -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

diff --git a/arch/x86_64/lib/rwlock.S b/arch/x86_64/lib/rwlock.S
new file mode 100644 (file)
index 0000000..0cde1f8
--- /dev/null
+++ b/arch/x86_64/lib/rwlock.S
@@ -0,0 +1,38 @@
+/* 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)

diff --git a/arch/x86_64/lib/thunk.S b/arch/x86_64/lib/thunk.S
index 332ea5d..6cff27c 100644 (file)
--- a/arch/x86_64/lib/thunk.S
+++ b/arch/x86_64/lib/thunk.S
@@ -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

diff --git a/include/asm-x86_64/rwlock.h b/include/asm-x86_64/rwlock.h
index dea0e94..28a080d 100644 (file)
--- a/include/asm-x86_64/rwlock.h
+++ b/include/asm-x86_64/rwlock.h
@@ -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

diff --git a/include/asm-x86_64/spinlock.h b/include/asm-x86_64/spinlock.h
index 248a79f..a8e3d89 100644 (file)
--- a/include/asm-x86_64/spinlock.h
+++ b/include/asm-x86_64/spinlock.h
@@ -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)