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documentation: Remove obsolete reference to RCU-protected indexes 

Commit #1ebee8017d84 (rcu: Eliminate array-index-based RCU primitives)
eliminated the primitives supporting RCU-protected array indexes, but
failed to update Documentation/memory-barriers.txt accordingly.  This
commit therefore removes the discussion of RCU-protected array indexes.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
steinar/wifi_calib_4_9_kernel
Paul E. McKenney 2016-01-14 14:01:34 -08:00
parent 895f554222
commit 0e4bd2aba3
1 changed files with 0 additions and 15 deletions
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Documentation/memory-barriers.txt
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@ -565,21 +565,6 @@ odd-numbered bank is idle, one can see the new value of the pointer P (&B),
but the old value of the variable B (2).
Another example of where data dependency barriers might be required is where a
number is read from memory and then used to calculate the index for an array
access:
CPU 1 CPU 2
=============== ===============
{ M[0] == 1, M[1] == 2, M[3] = 3, P == 0, Q == 3 }
M[1] = 4;
<write barrier>
WRITE_ONCE(P, 1);
Q = READ_ONCE(P);
<data dependency barrier>
D = M[Q];
The data dependency barrier is very important to the RCU system,
for example. See rcu_assign_pointer() and rcu_dereference() in
include/linux/rcupdate.h. This permits the current target of an RCU'd