Commit 3f379b03 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Ingo Molnar
Browse files

ftrace: Replace read_barrier_depends() with rcu_dereference_raw()

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: default avatarPaul E. McKenney <>
Acked-by: default avatarSteven Rostedt <>
Cc: Frederic Weisbecker <>
LKML-Reference: <>
Signed-off-by: default avatarIngo Molnar <>
parent 54dbf96c
......@@ -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);
* 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! */
struct ftrace_ops *op = rcu_dereference_raw(ftrace_list); /*see above*/
while (op != &ftrace_list_end) {
/* silly alpha */
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.
ftrace_list = ops;
rcu_assign_pointer(ftrace_list, ops);
if (ftrace_enabled) {
ftrace_func_t func;
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