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A recent change in kernel/acct.c added a new warning for many configurations on ARM: kernel/acct.c: In function 'acct_pin_kill': arch/arm/include/asm/cmpxchg.h:122:3: warning: value computed is not used [-Wunused-value] The code is in fact correct, it's just a cmpxchg() call that intentionally ignores the result, and no other code does that. The warning does not show up on x86 because of the way that its cmpxchg() macro is written. This changes the ARM implementation to use a similar construct with a compound expression instead of a typecast, which causes the compiler to not complain about an unused result. Fix the other macros in this file in a similar way, and place them just below their function implementations. Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
298 lines
6.4 KiB
C
298 lines
6.4 KiB
C
#ifndef __ASM_ARM_CMPXCHG_H
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#define __ASM_ARM_CMPXCHG_H
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#include <linux/irqflags.h>
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#include <linux/prefetch.h>
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#include <asm/barrier.h>
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#if defined(CONFIG_CPU_SA1100) || defined(CONFIG_CPU_SA110)
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/*
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* On the StrongARM, "swp" is terminally broken since it bypasses the
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* cache totally. This means that the cache becomes inconsistent, and,
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* since we use normal loads/stores as well, this is really bad.
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* Typically, this causes oopsen in filp_close, but could have other,
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* more disastrous effects. There are two work-arounds:
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* 1. Disable interrupts and emulate the atomic swap
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* 2. Clean the cache, perform atomic swap, flush the cache
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*
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* We choose (1) since its the "easiest" to achieve here and is not
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* dependent on the processor type.
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*
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* NOTE that this solution won't work on an SMP system, so explcitly
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* forbid it here.
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*/
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#define swp_is_buggy
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#endif
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static inline unsigned long __xchg(unsigned long x, volatile void *ptr, int size)
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{
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extern void __bad_xchg(volatile void *, int);
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unsigned long ret;
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#ifdef swp_is_buggy
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unsigned long flags;
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#endif
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#if __LINUX_ARM_ARCH__ >= 6
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unsigned int tmp;
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#endif
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smp_mb();
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prefetchw((const void *)ptr);
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switch (size) {
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#if __LINUX_ARM_ARCH__ >= 6
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case 1:
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asm volatile("@ __xchg1\n"
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"1: ldrexb %0, [%3]\n"
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" strexb %1, %2, [%3]\n"
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" teq %1, #0\n"
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" bne 1b"
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: "=&r" (ret), "=&r" (tmp)
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: "r" (x), "r" (ptr)
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: "memory", "cc");
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break;
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case 4:
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asm volatile("@ __xchg4\n"
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"1: ldrex %0, [%3]\n"
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" strex %1, %2, [%3]\n"
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" teq %1, #0\n"
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" bne 1b"
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: "=&r" (ret), "=&r" (tmp)
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: "r" (x), "r" (ptr)
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: "memory", "cc");
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break;
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#elif defined(swp_is_buggy)
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#ifdef CONFIG_SMP
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#error SMP is not supported on this platform
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#endif
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case 1:
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raw_local_irq_save(flags);
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ret = *(volatile unsigned char *)ptr;
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*(volatile unsigned char *)ptr = x;
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raw_local_irq_restore(flags);
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break;
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case 4:
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raw_local_irq_save(flags);
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ret = *(volatile unsigned long *)ptr;
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*(volatile unsigned long *)ptr = x;
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raw_local_irq_restore(flags);
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break;
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#else
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case 1:
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asm volatile("@ __xchg1\n"
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" swpb %0, %1, [%2]"
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: "=&r" (ret)
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: "r" (x), "r" (ptr)
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: "memory", "cc");
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break;
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case 4:
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asm volatile("@ __xchg4\n"
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" swp %0, %1, [%2]"
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: "=&r" (ret)
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: "r" (x), "r" (ptr)
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: "memory", "cc");
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break;
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#endif
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default:
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/* Cause a link-time error, the xchg() size is not supported */
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__bad_xchg(ptr, size), ret = 0;
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break;
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}
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smp_mb();
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return ret;
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}
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#define xchg(ptr, x) ({ \
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(__typeof__(*(ptr)))__xchg((unsigned long)(x), (ptr), \
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sizeof(*(ptr))); \
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})
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#include <asm-generic/cmpxchg-local.h>
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#if __LINUX_ARM_ARCH__ < 6
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/* min ARCH < ARMv6 */
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#ifdef CONFIG_SMP
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#error "SMP is not supported on this platform"
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#endif
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/*
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* cmpxchg_local and cmpxchg64_local are atomic wrt current CPU. Always make
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* them available.
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*/
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#define cmpxchg_local(ptr, o, n) ({ \
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(__typeof(*ptr))__cmpxchg_local_generic((ptr), \
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(unsigned long)(o), \
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(unsigned long)(n), \
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sizeof(*(ptr))); \
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})
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#define cmpxchg64_local(ptr, o, n) __cmpxchg64_local_generic((ptr), (o), (n))
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#include <asm-generic/cmpxchg.h>
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#else /* min ARCH >= ARMv6 */
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extern void __bad_cmpxchg(volatile void *ptr, int size);
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/*
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* cmpxchg only support 32-bits operands on ARMv6.
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*/
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static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
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unsigned long new, int size)
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{
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unsigned long oldval, res;
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prefetchw((const void *)ptr);
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switch (size) {
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#ifndef CONFIG_CPU_V6 /* min ARCH >= ARMv6K */
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case 1:
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do {
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asm volatile("@ __cmpxchg1\n"
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" ldrexb %1, [%2]\n"
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" mov %0, #0\n"
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" teq %1, %3\n"
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" strexbeq %0, %4, [%2]\n"
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: "=&r" (res), "=&r" (oldval)
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: "r" (ptr), "Ir" (old), "r" (new)
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: "memory", "cc");
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} while (res);
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break;
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case 2:
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do {
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asm volatile("@ __cmpxchg1\n"
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" ldrexh %1, [%2]\n"
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" mov %0, #0\n"
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" teq %1, %3\n"
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" strexheq %0, %4, [%2]\n"
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: "=&r" (res), "=&r" (oldval)
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: "r" (ptr), "Ir" (old), "r" (new)
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: "memory", "cc");
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} while (res);
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break;
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#endif
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case 4:
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do {
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asm volatile("@ __cmpxchg4\n"
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" ldrex %1, [%2]\n"
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" mov %0, #0\n"
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" teq %1, %3\n"
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" strexeq %0, %4, [%2]\n"
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: "=&r" (res), "=&r" (oldval)
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: "r" (ptr), "Ir" (old), "r" (new)
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: "memory", "cc");
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} while (res);
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break;
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default:
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__bad_cmpxchg(ptr, size);
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oldval = 0;
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}
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return oldval;
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}
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static inline unsigned long __cmpxchg_mb(volatile void *ptr, unsigned long old,
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unsigned long new, int size)
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{
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unsigned long ret;
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smp_mb();
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ret = __cmpxchg(ptr, old, new, size);
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smp_mb();
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return ret;
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}
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#define cmpxchg(ptr,o,n) ({ \
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(__typeof__(*(ptr)))__cmpxchg_mb((ptr), \
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(unsigned long)(o), \
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(unsigned long)(n), \
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sizeof(*(ptr))); \
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})
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static inline unsigned long __cmpxchg_local(volatile void *ptr,
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unsigned long old,
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unsigned long new, int size)
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{
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unsigned long ret;
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switch (size) {
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#ifdef CONFIG_CPU_V6 /* min ARCH == ARMv6 */
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case 1:
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case 2:
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ret = __cmpxchg_local_generic(ptr, old, new, size);
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break;
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#endif
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default:
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ret = __cmpxchg(ptr, old, new, size);
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}
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return ret;
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}
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#define cmpxchg_local(ptr, o, n) ({ \
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(__typeof(*ptr))__cmpxchg_local((ptr), \
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(unsigned long)(o), \
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(unsigned long)(n), \
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sizeof(*(ptr))); \
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})
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static inline unsigned long long __cmpxchg64(unsigned long long *ptr,
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unsigned long long old,
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unsigned long long new)
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{
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unsigned long long oldval;
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unsigned long res;
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prefetchw(ptr);
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__asm__ __volatile__(
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"1: ldrexd %1, %H1, [%3]\n"
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" teq %1, %4\n"
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" teqeq %H1, %H4\n"
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" bne 2f\n"
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" strexd %0, %5, %H5, [%3]\n"
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" teq %0, #0\n"
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" bne 1b\n"
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"2:"
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: "=&r" (res), "=&r" (oldval), "+Qo" (*ptr)
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: "r" (ptr), "r" (old), "r" (new)
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: "cc");
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return oldval;
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}
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#define cmpxchg64_relaxed(ptr, o, n) ({ \
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(__typeof__(*(ptr)))__cmpxchg64((ptr), \
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(unsigned long long)(o), \
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(unsigned long long)(n)); \
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})
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#define cmpxchg64_local(ptr, o, n) cmpxchg64_relaxed((ptr), (o), (n))
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static inline unsigned long long __cmpxchg64_mb(unsigned long long *ptr,
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unsigned long long old,
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unsigned long long new)
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{
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unsigned long long ret;
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smp_mb();
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ret = __cmpxchg64(ptr, old, new);
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smp_mb();
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return ret;
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}
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#define cmpxchg64(ptr, o, n) ({ \
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(__typeof__(*(ptr)))__cmpxchg64_mb((ptr), \
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(unsigned long long)(o), \
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(unsigned long long)(n)); \
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})
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#endif /* __LINUX_ARM_ARCH__ >= 6 */
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#endif /* __ASM_ARM_CMPXCHG_H */
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