Merge branch 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel...

[linux-2.6-block.git] / kernel / trace / ftrace.c

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index bb53edbb5c8c7fc7a8f4a4f2db423aa1512b2a43..d9062f5cc0c01e598670d651fba80b87ccb68a57 100644 (file)
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -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>
 
@@ -84,18 +85,22 @@ ftrace_func_t ftrace_trace_function __read_mostly = ftrace_stub;
 ftrace_func_t __ftrace_trace_function __read_mostly = ftrace_stub;
 ftrace_func_t ftrace_pid_function __read_mostly = ftrace_stub;
 
+/*
+ * 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*/
        };
 }
 
@@ -150,8 +155,7 @@ 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;