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x86: fix IO write barrier 

wmb() on x86 must always include a barrier, because stores can go out of
order in many cases when dealing with devices (eg. WC memory).

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Nick Piggin 2007-10-13 03:06:55 +02:00 committed by Linus Torvalds
parent df1bdc0667
commit 4071c71855
2 changed files with 7 additions and 14 deletions
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15
include/asm-x86/system_32.h
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@ -216,6 +216,7 @@ static inline unsigned long get_limit(unsigned long segment)
#define mb() alternative("lock; addl $0,0(%%esp)", "mfence", X86_FEATURE_XMM2)
#define rmb() alternative("lock; addl $0,0(%%esp)", "lfence", X86_FEATURE_XMM2)
#define wmb() alternative("lock; addl $0,0(%%esp)", "sfence", X86_FEATURE_XMM)
/**
* read_barrier_depends - Flush all pending reads that subsequents reads
@ -271,18 +272,14 @@ static inline unsigned long get_limit(unsigned long segment)
#define read_barrier_depends() do { } while(0)
#ifdef CONFIG_X86_OOSTORE
/* Actually there are no OOO store capable CPUs for now that do SSE,
but make it already an possibility. */
#define wmb() alternative("lock; addl $0,0(%%esp)", "sfence", X86_FEATURE_XMM)
#else
#define wmb() __asm__ __volatile__ ("": : :"memory")
#endif
#ifdef CONFIG_SMP
#define smp_mb() mb()
#define smp_rmb() rmb()
#define smp_wmb() wmb()
#ifdef CONFIG_X86_OOSTORE
# define smp_wmb() wmb()
#else
# define smp_wmb() barrier()
#endif
#define smp_read_barrier_depends() read_barrier_depends()
#define set_mb(var, value) do { (void) xchg(&var, value); } while (0)
#else

6
include/asm-x86/system_64.h
View File

@ -159,12 +159,8 @@ static inline void write_cr8(unsigned long val)
*/
#define mb() asm volatile("mfence":::"memory")
#define rmb() asm volatile("lfence":::"memory")
#ifdef CONFIG_UNORDERED_IO
#define wmb() asm volatile("sfence" ::: "memory")
#else
#define wmb() asm volatile("" ::: "memory")
#endif
#define read_barrier_depends() do {} while(0)
#define set_mb(var, value) do { (void) xchg(&var, value); } while (0)