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target: encapsulate smp_mb__after_atomic()

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The target code has a rather generous helping of smp_mb__after_atomic()
throughout the code base.  Most atomic operations were followed by one
and none were preceded by smp_mb__before_atomic(), nor accompanied by a
comment explaining the need for a barrier.

Instead of trying to prove for every case whether or not it is needed,
this patch introduces atomic_inc_mb() and atomic_dec_mb(), which
explicitly include the memory barriers before and after the atomic
operation.  For now they are defined in a target header, although they
could be of general use.

Most of the existing atomic/mb combinations were replaced by the new
helpers.  In a few cases the atomic was sandwiched in
spin_lock/spin_unlock and I simply removed the barrier.

I suspect that in most cases the correct conversion would have been to
drop the barrier.  I also suspect that a few cases exist where a) the
barrier was necessary and b) a second barrier before the atomic would
have been necessary and got added by this patch.

Signed-off-by: Joern Engel <joern@logfs.org>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
This commit is contained in:
Joern Engel
2014-09-16 16:23:12 -04:00
committed by Nicholas Bellinger
parent 74ed7e6228
commit 33940d0993
7 changed files with 70 additions and 115 deletions
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14
include/target/target_core_base.h
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@ -903,4 +903,18 @@ struct se_wwn {
struct config_group fabric_stat_group;
};
static inline void atomic_inc_mb(atomic_t *v)
{
smp_mb__before_atomic();
atomic_inc(v);
smp_mb__after_atomic();
}
static inline void atomic_dec_mb(atomic_t *v)
{
smp_mb__before_atomic();
atomic_dec(v);
smp_mb__after_atomic();
}
#endif /* TARGET_CORE_BASE_H */