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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2010-08-19 21:43:09 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2010-08-20 09:00:18 -0700
commit65e6bf484c497f02d47a0faae69ee398cd59cfda (patch)
tree644a86b779a196da7c050cde9de593c413e0cc1e
parent80dcf60e6b97c7363971e7a0a788d8484d35f8a6 (diff)
rcu: add comment stating that list_empty() applies to RCU-protected lists
Because list_empty() does not dereference any RCU-protected pointers, and further does not pass such pointers to the caller (so that the caller does not dereference them either), it is safe to use list_empty() on RCU-protected lists. There is no need for a list_empty_rcu(). This commit adds a comment stating this explicitly. Requested-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
-rw-r--r--include/linux/rculist.h9
1 files changed, 9 insertions, 0 deletions
diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index c10b1050dbe6..f31ef61f1c65 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -10,6 +10,15 @@
#include <linux/rcupdate.h>
/*
+ * Why is there no list_empty_rcu()? Because list_empty() serves this
+ * purpose. The list_empty() function fetches the RCU-protected pointer
+ * and compares it to the address of the list head, but neither dereferences
+ * this pointer itself nor provides this pointer to the caller. Therefore,
+ * it is not necessary to use rcu_dereference(), so that list_empty() can
+ * be used anywhere you would want to use a list_empty_rcu().
+ */
+
+/*
* return the ->next pointer of a list_head in an rcu safe
* way, we must not access it directly
*/