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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>
hifive-unleashed-5.1
Paul E. McKenney 2010-08-19 21:43:09 -07:00
parent 80dcf60e6b
commit 65e6bf484c
1 changed files with 9 additions and 0 deletions
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9
include/linux/rculist.h
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@ -9,6 +9,15 @@
#include <linux/list.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
* way, we must not access it directly