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locking/barriers: Add implicit smp_read_barrier_depends() to READ_ONCE()

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In preparation for the removal of lockless_dereference(), which is the
same as READ_ONCE() on all architectures other than Alpha, add an
implicit smp_read_barrier_depends() to READ_ONCE() so that it can be
used to head dependency chains on all architectures.

Signed-off-by: Will Deacon <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Will Deacon authored and Ingo Molnar committed 2017-10-24 13:17:32 +02:00
1 parent d15155824c
commit 76ebbe78f7
1 file changed
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include/linux/compiler.h
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@@ -242,6 +242,7 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
__read_once_size(&(x), __u.__c, sizeof(x)); \
else \
__read_once_size_nocheck(&(x), __u.__c, sizeof(x)); \
smp_read_barrier_depends(); /* Enforce dependency ordering from x */ \
__u.__val; \
})
#define READ_ONCE(x) __READ_ONCE(x, 1)