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Commit 65e6bf48 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 80dcf60e

include/linux/rculist.h

+9 −0
Original line number Original line Diff line number Diff line
@@ -9,6 +9,15 @@ 
#include <linux/list.h>

#include <linux/list.h>

#include <linux/rcupdate.h>

#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

 * return the ->next pointer of a list_head in an rcu safe

 * way, we must not access it directly

 * way, we must not access it directly