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Re: cmpxchg broken in some situation

To: Ralf Baechle <ralf@linux-mips.org>
Subject: Re: cmpxchg broken in some situation
From: Fuxin Zhang <fxzhang@ict.ac.cn>
Date: Wed, 03 Oct 2007 06:48:28 +0800
Cc: linux-mips@linux-mips.org
In-reply-to: <20071002103551.GB5152@linux-mips.org>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <46FF7BC2.5050905@ict.ac.cn> <20071001025340.GA7091@linux-mips.org> <47010E15.7060109@ict.ac.cn> <20071001152620.GB15820@linux-mips.org> <470210B4.8020902@ict.ac.cn> <20071002103551.GB5152@linux-mips.org>
Sender: linux-mips-bounce@linux-mips.org
User-agent: IceDove 1.5.0.10 (X11/20070329)
And the comment "# cmpxchg_u32" is out of date too:)

Ralf Baechle 写道:
On Tue, Oct 02, 2007 at 05:34:44PM +0800, Fuxin Zhang wrote:

The problem is here:

switch (sizeof(__ptr)) { // --> should be sizeof(*(__ptr))
case 4:
...
Recompiling..

There was another small kink, cmpxchg_local() does not imply a memory
barrier so I optimized that case.

And I don't complain about it being 151 lines shorter ;-)

  Ralf

From: Ralf Baechle <ralf@linux-mips.org>

[MIPS] Typeproof reimplementation of cmpxchg.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

diff --git a/include/asm-mips/cmpxchg.h b/include/asm-mips/cmpxchg.h
new file mode 100644
index 0000000..46bac47
--- /dev/null
+++ b/include/asm-mips/cmpxchg.h
@@ -0,0 +1,107 @@
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 2003, 06, 07 by Ralf Baechle (ralf@linux-mips.org)
+ */
+#ifndef __ASM_CMPXCHG_H
+#define __ASM_CMPXCHG_H
+
+#include <linux/irqflags.h>
+
+#define __HAVE_ARCH_CMPXCHG 1
+
+#define __cmpxchg_asm(ld, st, m, old, new)                             \
+({                                                                     \
+       __typeof(*(m)) __ret;                                           \
+                                                                       \
+       if (cpu_has_llsc && R10000_LLSC_WAR) {                          \
+               __asm__ __volatile__(                                   \
+               "  .set    push                            \n"        \
+               "  .set    noat                            \n"        \
+               "  .set    mips3                           \n"        \
+               "1:        " ld "        %0, %2          # __cmpxchg_u32 \n"    
    \
+               "  bne     %0, %z3, 2f                     \n"        \
+               "  .set    mips0                           \n"        \
+               "  move    $1, %z4                         \n"        \
+               "  .set    mips3                           \n"        \
+               "  " st "        $1, %1                          \n"        \
+               "  beqzl   $1, 1b                          \n"        \
+               "2:                                                \n"        \
+               "  .set    pop                             \n"        \
+               : "=&r" (__ret), "=R" (*m)                              \
+               : "R" (*m), "Jr" (old), "Jr" (new)                        \
+               : "memory");                                          \
+       } else if (cpu_has_llsc) {                                      \
+               __asm__ __volatile__(                                   \
+               "  .set    push                            \n"        \
+               "  .set    noat                            \n"        \
+               "  .set    mips3                           \n"        \
+               "1:        " ld "        %0, %2          # __cmpxchg_u32 \n"    
    \
+               "  bne     %0, %z3, 2f                     \n"        \
+               "  .set    mips0                           \n"        \
+               "  move    $1, %z4                         \n"        \
+               "  .set    mips3                           \n"        \
+               "  " st "        $1, %1                          \n"        \
+               "  beqz    $1, 3f                          \n"        \
+               "2:                                                \n"        \
+               "  .subsection 2                           \n"        \
+               "3:        b       1b                              \n"        \
+               "  .previous                               \n"        \
+               "  .set    pop                             \n"        \
+               : "=&r" (__ret), "=R" (*m)                              \
+               : "R" (*m), "Jr" (old), "Jr" (new)                        \
+               : "memory");                                          \
+       } else {                                                        \
+               unsigned long __flags;                                  \
+                                                                       \
+               raw_local_irq_save(__flags);                            \
+               __ret = *m;                                             \
+               if (__ret == old)                                       \
+                       *m = new;                                       \
+               raw_local_irq_restore(__flags);                         \
+       }                                                               \
+                                                                       \
+       smp_llsc_mb();                                                  \
+                                                                       \
+       __ret;                                                          \
+})
+
+/*
+ * This function doesn't exist, so you'll get a linker error
+ * if something tries to do an invalid cmpxchg().
+ */
+extern void __cmpxchg_called_with_bad_pointer(void);
+
+#define __cmpxchg(ptr,old,new,barrier)                                 \
+({                                                                     \
+       __typeof__(ptr) __ptr = (ptr);                                  \
+       __typeof__(*(ptr)) __old = (old);                               \
+       __typeof__(*(ptr)) __new = (new);                               \
+       __typeof__(*(ptr)) __res = 0;                                   \
+                                                                       \
+       switch (sizeof(*(__ptr))) {                                     \
+       case 4:                                                         \
+               __res = __cmpxchg_asm("ll", "sc", __ptr, __old, __new);     \
+               break;                                                  \
+       case 8:                                                         \
+               if (sizeof(long) == 8) {                                \
+                       __res = __cmpxchg_asm("lld", "scd", __ptr,  \
+                                          __old, __new);               \
+                       break;                                          \
+               }                                                       \
+       default:                                                        \
+               __cmpxchg_called_with_bad_pointer();                    \
+               break;                                                  \
+       }                                                               \
+                                                                       \
+       barrier;                                                        \
+                                                                       \
+       __res;                                                          \
+})
+
+#define cmpxchg(ptr, old, new)         __cmpxchg(ptr, old, new, smp_llsc_mb())
+#define cmpxchg_local(ptr, old, new)   __cmpxchg(ptr, old, new,)
+
+#endif /* __ASM_CMPXCHG_H */
diff --git a/include/asm-mips/local.h b/include/asm-mips/local.h
index ed882c8..7034a01 100644
--- a/include/asm-mips/local.h
+++ b/include/asm-mips/local.h
@@ -4,6 +4,7 @@
 #include <linux/percpu.h>
 #include <linux/bitops.h>
 #include <asm/atomic.h>
+#include <asm/cmpxchg.h>
 #include <asm/war.h>
typedef struct
diff --git a/include/asm-mips/system.h b/include/asm-mips/system.h
index 357251f..480b574 100644
--- a/include/asm-mips/system.h
+++ b/include/asm-mips/system.h
@@ -17,6 +17,7 @@
#include <asm/addrspace.h>
 #include <asm/barrier.h>
+#include <asm/cmpxchg.h>
 #include <asm/cpu-features.h>
 #include <asm/dsp.h>
 #include <asm/war.h>
@@ -194,266 +195,6 @@ static inline unsigned long __xchg(unsigned long x, 
volatile void * ptr, int siz
#define xchg(ptr,x) ((__typeof__(*(ptr)))__xchg((unsigned long)(x),(ptr),sizeof(*(ptr)))) -#define __HAVE_ARCH_CMPXCHG 1
-
-static inline unsigned long __cmpxchg_u32(volatile int * m, unsigned long old,
-       unsigned long new)
-{
-       __u32 retval;
-
-       if (cpu_has_llsc && R10000_LLSC_WAR) {
-               __asm__ __volatile__(
-               "  .set    push                                    \n"
-               "  .set    noat                                    \n"
-               "  .set    mips3                                   \n"
-               "1:        ll      %0, %2                  # __cmpxchg_u32 \n"
-               "  bne     %0, %z3, 2f                             \n"
-               "  .set    mips0                                   \n"
-               "  move    $1, %z4                                 \n"
-               "  .set    mips3                                   \n"
-               "  sc      $1, %1                                  \n"
-               "  beqzl   $1, 1b                                  \n"
-               "2:                                                        \n"
-               "  .set    pop                                     \n"
-               : "=&r" (retval), "=R" (*m)
-               : "R" (*m), "Jr" (old), "Jr" (new)
-               : "memory");
-       } else if (cpu_has_llsc) {
-               __asm__ __volatile__(
-               "  .set    push                                    \n"
-               "  .set    noat                                    \n"
-               "  .set    mips3                                   \n"
-               "1:        ll      %0, %2                  # __cmpxchg_u32 \n"
-               "  bne     %0, %z3, 2f                             \n"
-               "  .set    mips0                                   \n"
-               "  move    $1, %z4                                 \n"
-               "  .set    mips3                                   \n"
-               "  sc      $1, %1                                  \n"
-               "  beqz    $1, 3f                                  \n"
-               "2:                                                        \n"
-               "  .subsection 2                                   \n"
-               "3:        b       1b                                      \n"
-               "  .previous                                       \n"
-               "  .set    pop                                     \n"
-               : "=&r" (retval), "=R" (*m)
-               : "R" (*m), "Jr" (old), "Jr" (new)
-               : "memory");
-       } else {
-               unsigned long flags;
-
-               raw_local_irq_save(flags);
-               retval = *m;
-               if (retval == old)
-                       *m = new;
-               raw_local_irq_restore(flags);   /* implies memory barrier  */
-       }
-
-       smp_llsc_mb();
-
-       return retval;
-}
-
-static inline unsigned long __cmpxchg_u32_local(volatile int * m,
-       unsigned long old, unsigned long new)
-{
-       __u32 retval;
-
-       if (cpu_has_llsc && R10000_LLSC_WAR) {
-               __asm__ __volatile__(
-               "  .set    push                                    \n"
-               "  .set    noat                                    \n"
-               "  .set    mips3                                   \n"
-               "1:        ll      %0, %2                  # __cmpxchg_u32 \n"
-               "  bne     %0, %z3, 2f                             \n"
-               "  .set    mips0                                   \n"
-               "  move    $1, %z4                                 \n"
-               "  .set    mips3                                   \n"
-               "  sc      $1, %1                                  \n"
-               "  beqzl   $1, 1b                                  \n"
-               "2:                                                        \n"
-               "  .set    pop                                     \n"
-               : "=&r" (retval), "=R" (*m)
-               : "R" (*m), "Jr" (old), "Jr" (new)
-               : "memory");
-       } else if (cpu_has_llsc) {
-               __asm__ __volatile__(
-               "  .set    push                                    \n"
-               "  .set    noat                                    \n"
-               "  .set    mips3                                   \n"
-               "1:        ll      %0, %2                  # __cmpxchg_u32 \n"
-               "  bne     %0, %z3, 2f                             \n"
-               "  .set    mips0                                   \n"
-               "  move    $1, %z4                                 \n"
-               "  .set    mips3                                   \n"
-               "  sc      $1, %1                                  \n"
-               "  beqz    $1, 1b                                  \n"
-               "2:                                                        \n"
-               "  .set    pop                                     \n"
-               : "=&r" (retval), "=R" (*m)
-               : "R" (*m), "Jr" (old), "Jr" (new)
-               : "memory");
-       } else {
-               unsigned long flags;
-
-               local_irq_save(flags);
-               retval = *m;
-               if (retval == old)
-                       *m = new;
-               local_irq_restore(flags);       /* implies memory barrier  */
-       }
-
-       return retval;
-}
-
-#ifdef CONFIG_64BIT
-static inline unsigned long __cmpxchg_u64(volatile int * m, unsigned long old,
-       unsigned long new)
-{
-       __u64 retval;
-
-       if (cpu_has_llsc && R10000_LLSC_WAR) {
-               __asm__ __volatile__(
-               "  .set    push                                    \n"
-               "  .set    noat                                    \n"
-               "  .set    mips3                                   \n"
-               "1:        lld     %0, %2                  # __cmpxchg_u64 \n"
-               "  bne     %0, %z3, 2f                             \n"
-               "  move    $1, %z4                                 \n"
-               "  scd     $1, %1                                  \n"
-               "  beqzl   $1, 1b                                  \n"
-               "2:                                                        \n"
-               "  .set    pop                                     \n"
-               : "=&r" (retval), "=R" (*m)
-               : "R" (*m), "Jr" (old), "Jr" (new)
-               : "memory");
-       } else if (cpu_has_llsc) {
-               __asm__ __volatile__(
-               "  .set    push                                    \n"
-               "  .set    noat                                    \n"
-               "  .set    mips3                                   \n"
-               "1:        lld     %0, %2                  # __cmpxchg_u64 \n"
-               "  bne     %0, %z3, 2f                             \n"
-               "  move    $1, %z4                                 \n"
-               "  scd     $1, %1                                  \n"
-               "  beqz    $1, 3f                                  \n"
-               "2:                                                        \n"
-               "  .subsection 2                                   \n"
-               "3:        b       1b                                      \n"
-               "  .previous                                       \n"
-               "  .set    pop                                     \n"
-               : "=&r" (retval), "=R" (*m)
-               : "R" (*m), "Jr" (old), "Jr" (new)
-               : "memory");
-       } else {
-               unsigned long flags;
-
-               raw_local_irq_save(flags);
-               retval = *m;
-               if (retval == old)
-                       *m = new;
-               raw_local_irq_restore(flags);   /* implies memory barrier  */
-       }
-
-       smp_llsc_mb();
-
-       return retval;
-}
-
-static inline unsigned long __cmpxchg_u64_local(volatile int * m,
-       unsigned long old, unsigned long new)
-{
-       __u64 retval;
-
-       if (cpu_has_llsc && R10000_LLSC_WAR) {
-               __asm__ __volatile__(
-               "  .set    push                                    \n"
-               "  .set    noat                                    \n"
-               "  .set    mips3                                   \n"
-               "1:        lld     %0, %2                  # __cmpxchg_u64 \n"
-               "  bne     %0, %z3, 2f                             \n"
-               "  move    $1, %z4                                 \n"
-               "  scd     $1, %1                                  \n"
-               "  beqzl   $1, 1b                                  \n"
-               "2:                                                        \n"
-               "  .set    pop                                     \n"
-               : "=&r" (retval), "=R" (*m)
-               : "R" (*m), "Jr" (old), "Jr" (new)
-               : "memory");
-       } else if (cpu_has_llsc) {
-               __asm__ __volatile__(
-               "  .set    push                                    \n"
-               "  .set    noat                                    \n"
-               "  .set    mips3                                   \n"
-               "1:        lld     %0, %2                  # __cmpxchg_u64 \n"
-               "  bne     %0, %z3, 2f                             \n"
-               "  move    $1, %z4                                 \n"
-               "  scd     $1, %1                                  \n"
-               "  beqz    $1, 1b                                  \n"
-               "2:                                                        \n"
-               "  .set    pop                                     \n"
-               : "=&r" (retval), "=R" (*m)
-               : "R" (*m), "Jr" (old), "Jr" (new)
-               : "memory");
-       } else {
-               unsigned long flags;
-
-               local_irq_save(flags);
-               retval = *m;
-               if (retval == old)
-                       *m = new;
-               local_irq_restore(flags);       /* implies memory barrier  */
-       }
-
-       return retval;
-}
-
-#else
-extern unsigned long __cmpxchg_u64_unsupported_on_32bit_kernels(
-       volatile int * m, unsigned long old, unsigned long new);
-#define __cmpxchg_u64 __cmpxchg_u64_unsupported_on_32bit_kernels
-extern unsigned long __cmpxchg_u64_local_unsupported_on_32bit_kernels(
-       volatile int * m, unsigned long old, unsigned long new);
-#define __cmpxchg_u64_local __cmpxchg_u64_local_unsupported_on_32bit_kernels
-#endif
-
-/* This function doesn't exist, so you'll get a linker error
-   if something tries to do an invalid cmpxchg().  */
-extern void __cmpxchg_called_with_bad_pointer(void);
-
-static inline unsigned long __cmpxchg(volatile void * ptr, unsigned long old,
-       unsigned long new, int size)
-{
-       switch (size) {
-       case 4:
-               return __cmpxchg_u32(ptr, old, new);
-       case 8:
-               return __cmpxchg_u64(ptr, old, new);
-       }
-       __cmpxchg_called_with_bad_pointer();
-       return old;
-}
-
-static inline unsigned long __cmpxchg_local(volatile void * ptr,
-       unsigned long old, unsigned long new, int size)
-{
-       switch (size) {
-       case 4:
-               return __cmpxchg_u32_local(ptr, old, new);
-       case 8:
-               return __cmpxchg_u64_local(ptr, old, new);
-       }
-       __cmpxchg_called_with_bad_pointer();
-       return old;
-}
-
-#define cmpxchg(ptr,old,new) \
-       ((__typeof__(*(ptr)))__cmpxchg((ptr), \
-               (unsigned long)(old), (unsigned long)(new),sizeof(*(ptr))))
-
-#define cmpxchg_local(ptr,old,new) \
-       ((__typeof__(*(ptr)))__cmpxchg_local((ptr), \
-               (unsigned long)(old), (unsigned long)(new),sizeof(*(ptr))))
-
 extern void set_handler (unsigned long offset, void *addr, unsigned long len);
 extern void set_uncached_handler (unsigned long offset, void *addr, unsigned 
long len);



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