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Commit 4071c718 authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
Browse files

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: default avatarNick Piggin <npiggin@suse.de>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent df1bdc06

include/asm-x86/system_32.h

+6 −9
Original line number Diff line number Diff line
@@ -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()

#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

include/asm-x86/system_64.h

+1 −5
Original line number Diff line number Diff line
@@ -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)