linux-3.3/Documentation/atomic_ops.txt

37 proper implicit or explicit read memory barrier is needed before reading the
55 or explicit memory barrier is needed before the value set with the operation
65 implicit or explicit memory barrier is used after possible runtime
69 interface must take care of that with a proper implicit or explicit memory
79 or processor, and explicitly invoke the appropriate compiler and/or memory
146 and never changed later, so that memory barriers are not needed:
169 Don't even -think- about doing this without proper use of memory barriers,
188 require any explicit memory barriers.  They need only perform the
200 Unlike the above routines, it is required that explicit memory
202 done such that all memory operations before and after the atomic
210 memory barrier semantics which satisfy the above requirements, that is
220 This means that like atomic_{inc,dec}_return(), the memory barrier
232 It requires explicit memory barrier semantics around the operation as
239 memory barrier semantics around the operation.
245 is negative.  It requires explicit memory barrier semantics around the
263 atomic_cmpxchg requires explicit memory barriers around the operation.
276 atomic_add_unless requires explicit memory barriers around the operation
282 If a caller requires memory barrier semantics around an atomic_t
297 It makes sure that all memory operations preceding the atomic_dec()
308 ordering with respect to memory operations after an atomic_dec() call
312 A missing memory barrier in the cases where they are required by the
376  found a bug wrt. memory barriers in kfree_skb() that exposed
377  the atomic_t memory barrier requirements quite clearly.)
403 With the memory barrier semantics required of the atomic_t operations
404 which return values, the above sequence of memory visibility can never
423 their SMP and memory barrier semantics are similar in shape and scope
438 They must execute atomically, yet there are no implicit memory barrier
464 require explicit memory barrier semantics around their execution.  All
465 memory operations before the atomic bit operation call must be made
468 subsequent memory operation is made visible.  For example:
476 "obj->dead = 1;" is visible to cpus before the atomic memory operation
478 memory operation done by test_and_set_bit() must become visible before
488 If explicit memory barriers are required around clear_bit() (which
489 does not return a value, and thus does not need to provide memory
498 	/* All memory operations before this call will
505 	 * subsequent memory operations.
537 These non-atomic variants also do not require any special memory
540 The routines xchg() and cmpxchg() need the same exact memory barriers
543 Spinlocks and rwlocks have memory barrier expectations as well.
547    visible before any subsequent memory operation.
550    all previous memory operations are globally visible before the
564 It is actually pretty simple to get the memory barrier correct.
567 subsequent memory operation.
624 Now, as far as memory barriers go, as long as spin_lock()
625 strictly orders all subsequent memory operations (including
633 is not dropping to zero, there are no memory ordering