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ftrace: Replace read_barrier_depends() with rcu_dereference_raw()

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Replace the calls to read_barrier_depends() in
ftrace_list_func() with rcu_dereference_raw() to improve
readability.  The reason that we use rcu_dereference_raw() here
is that removed entries are never freed, instead they are simply
leaked.  This is one of a very few cases where use of
rcu_dereference_raw() is the long-term right answer.  And I
don't yet know of any others.  ;-)

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <1267830207-9474-1-git-send-email-paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Paul E. McKenney 2010-03-05 15:03:25 -08:00 committed by Ingo Molnar
parent 54dbf96c92
commit 3f379b03fb
1 changed files with 13 additions and 9 deletions
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22
kernel/trace/ftrace.c
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@ -27,6 +27,7 @@
#include <linux/ctype.h>
#include <linux/list.h>
#include <linux/hash.h>
#include <linux/rcupdate.h>
#include <trace/events/sched.h>
@ -88,18 +89,22 @@ ftrace_func_t ftrace_pid_function __read_mostly = ftrace_stub;
static int ftrace_set_func(unsigned long *array, int *idx, char *buffer);
#endif
/*
* Traverse the ftrace_list, invoking all entries. The reason that we
* can use rcu_dereference_raw() is that elements removed from this list
* are simply leaked, so there is no need to interact with a grace-period
* mechanism. The rcu_dereference_raw() calls are needed to handle
* concurrent insertions into the ftrace_list.
*
* Silly Alpha and silly pointer-speculation compiler optimizations!
*/
static void ftrace_list_func(unsigned long ip, unsigned long parent_ip)
{
struct ftrace_ops *op = ftrace_list;
/* in case someone actually ports this to alpha! */
read_barrier_depends();
struct ftrace_ops *op = rcu_dereference_raw(ftrace_list); /*see above*/
while (op != &ftrace_list_end) {
/* silly alpha */
read_barrier_depends();
op->func(ip, parent_ip);
op = op->next;
op = rcu_dereference_raw(op->next); /*see above*/
};
}
@ -154,8 +159,7 @@ static int __register_ftrace_function(struct ftrace_ops *ops)
* the ops->next pointer is valid before another CPU sees
* the ops pointer included into the ftrace_list.
*/
smp_wmb();
ftrace_list = ops;
rcu_assign_pointer(ftrace_list, ops);
if (ftrace_enabled) {
ftrace_func_t func;