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authorPaul E. McKenney <paulmck@kernel.org>2020-09-25 06:53:25 +0300
committerPaul E. McKenney <paulmck@kernel.org>2020-11-03 04:07:15 +0300
commit86b5a7381b12b1d1d5558d8087e5bbd04b7cf702 (patch)
treec4feed5f8bb666b4e18332112e6710950190fd6a /Documentation/RCU/checklist.rst
parent3650b228f83adda7e5ee532e2b90429c03f7b9ec (diff)
downloadlinux-86b5a7381b12b1d1d5558d8087e5bbd04b7cf702.tar.xz
doc: Present the role of READ_ONCE()
This commit adds an explanation of the special cases where READ_ONCE() may be used in place of a member of the rcu_dereference() family. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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diff --git a/Documentation/RCU/checklist.rst b/Documentation/RCU/checklist.rst
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+++ b/Documentation/RCU/checklist.rst
@@ -314,6 +314,13 @@ over a rather long period of time, but improvements are always welcome!
shared between readers and updaters. Additional primitives
are provided for this case, as discussed in lockdep.txt.
+ One exception to this rule is when data is only ever added to
+ the linked data structure, and is never removed during any
+ time that readers might be accessing that structure. In such
+ cases, READ_ONCE() may be used in place of rcu_dereference()
+ and the read-side markers (rcu_read_lock() and rcu_read_unlock(),
+ for example) may be omitted.
+
10. Conversely, if you are in an RCU read-side critical section,
and you don't hold the appropriate update-side lock, you -must-
use the "_rcu()" variants of the list macros. Failing to do so