[PATCH 30/31] arch,doc: Convert smp_mb__*

[Peter Zijlstra <peterz@infradead.org>]

[-- Attachment #1: peterz-doc-smp_mb__atomic.patch --]
[-- Type: text/plain, Size: 6061 bytes --]

Update the documentation to reflect the change of barrier primitives.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
---
 Documentation/atomic_ops.txt      |   31 ++++++++++----------------
 Documentation/memory-barriers.txt |   44 ++++++++++----------------------------
 2 files changed, 24 insertions(+), 51 deletions(-)

--- a/Documentation/atomic_ops.txt
+++ b/Documentation/atomic_ops.txt
@@ -285,15 +285,13 @@ If a caller requires memory barrier sema
 operation which does not return a value, a set of interfaces are
 defined which accomplish this:
 
-	void smp_mb__before_atomic_dec(void);
-	void smp_mb__after_atomic_dec(void);
-	void smp_mb__before_atomic_inc(void);
-	void smp_mb__after_atomic_inc(void);
+	void smp_mb__before_atomic(void);
+	void smp_mb__after_atomic(void);
 
-For example, smp_mb__before_atomic_dec() can be used like so:
+For example, smp_mb__before_atomic() can be used like so:
 
 	obj->dead = 1;
-	smp_mb__before_atomic_dec();
+	smp_mb__before_atomic();
 	atomic_dec(&obj->ref_count);
 
 It makes sure that all memory operations preceding the atomic_dec()
@@ -302,15 +300,10 @@ operation.  In the above example, it gua
 "1" to obj->dead will be globally visible to other cpus before the
 atomic counter decrement.
 
-Without the explicit smp_mb__before_atomic_dec() call, the
+Without the explicit smp_mb__before_atomic() call, the
 implementation could legally allow the atomic counter update visible
 to other cpus before the "obj->dead = 1;" assignment.
 
-The other three interfaces listed are used to provide explicit
-ordering with respect to memory operations after an atomic_dec() call
-(smp_mb__after_atomic_dec()) and around atomic_inc() calls
-(smp_mb__{before,after}_atomic_inc()).
-
 A missing memory barrier in the cases where they are required by the
 atomic_t implementation above can have disastrous results.  Here is
 an example, which follows a pattern occurring frequently in the Linux
@@ -487,12 +480,12 @@ memory operation done by test_and_set_bi
 Which returns a boolean indicating if bit "nr" is set in the bitmask
 pointed to by "addr".
 
-If explicit memory barriers are required around clear_bit() (which
-does not return a value, and thus does not need to provide memory
-barrier semantics), two interfaces are provided:
+If explicit memory barriers are required around {set,clear}_bit() (which do
+not return a value, and thus does not need to provide memory barrier
+semantics), two interfaces are provided:
 
-	void smp_mb__before_clear_bit(void);
-	void smp_mb__after_clear_bit(void);
+	void smp_mb__before_atomic(void);
+	void smp_mb__after_atomic(void);
 
 They are used as follows, and are akin to their atomic_t operation
 brothers:
@@ -500,13 +493,13 @@ They are used as follows, and are akin t
 	/* All memory operations before this call will
 	 * be globally visible before the clear_bit().
 	 */
-	smp_mb__before_clear_bit();
+	smp_mb__before_atomic();
 	clear_bit( ... );
 
 	/* The clear_bit() will be visible before all
 	 * subsequent memory operations.
 	 */
-	 smp_mb__after_clear_bit();
+	 smp_mb__after_atomic();
 
 There are two special bitops with lock barrier semantics (acquire/release,
 same as spinlocks). These operate in the same way as their non-_lock/unlock
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -1583,20 +1583,21 @@ CPU from reordering them.
      insert anything more than a compiler barrier in a UP compilation.
 
 
- (*) smp_mb__before_atomic_dec();
- (*) smp_mb__after_atomic_dec();
- (*) smp_mb__before_atomic_inc();
- (*) smp_mb__after_atomic_inc();
-
-     These are for use with atomic add, subtract, increment and decrement
-     functions that don't return a value, especially when used for reference
-     counting.  These functions do not imply memory barriers.
+ (*) smp_mb__before_atomic();
+ (*) smp_mb__after_atomic();
+
+     These are for use with atomic (such as add, subtract, increment and
+     decrement) functions that don't return a value, especially when used for
+     reference counting.  These functions do not imply memory barriers.
+
+     These are also used for atomic bitop functions that do not return a
+     value (such as set_bit and clear_bit).
 
      As an example, consider a piece of code that marks an object as being dead
      and then decrements the object's reference count:
 
 	obj->dead = 1;
-	smp_mb__before_atomic_dec();
+	smp_mb__before_atomic();
 	atomic_dec(&obj->ref_count);
 
      This makes sure that the death mark on the object is perceived to be set
@@ -1606,27 +1607,6 @@ CPU from reordering them.
      operations" subsection for information on where to use these.
 
 
- (*) smp_mb__before_clear_bit(void);
- (*) smp_mb__after_clear_bit(void);
-
-     These are for use similar to the atomic inc/dec barriers.  These are
-     typically used for bitwise unlocking operations, so care must be taken as
-     there are no implicit memory barriers here either.
-
-     Consider implementing an unlock operation of some nature by clearing a
-     locking bit.  The clear_bit() would then need to be barriered like this:
-
-	smp_mb__before_clear_bit();
-	clear_bit( ... );
-
-     This prevents memory operations before the clear leaking to after it.  See
-     the subsection on "Locking Functions" with reference to RELEASE operation
-     implications.
-
-     See Documentation/atomic_ops.txt for more information.  See the "Atomic
-     operations" subsection for information on where to use these.
-
-
 MMIO WRITE BARRIER
 ------------------
 
@@ -2283,11 +2263,11 @@ barriers, but might be used for implemen
 	change_bit();
 
 With these the appropriate explicit memory barrier should be used if necessary
-(smp_mb__before_clear_bit() for instance).
+(smp_mb__before_atomic() for instance).
 
 
 The following also do _not_ imply memory barriers, and so may require explicit
-memory barriers under some circumstances (smp_mb__before_atomic_dec() for
+memory barriers under some circumstances (smp_mb__before_atomic() for
 instance):
 
 	atomic_add();