The patch below does not apply to the 3.4-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
>From a4c35ed241129dd142be4cadb1e5a474a56d5464 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (Red Hat)" <rostedt@xxxxxxxxxxx>
Date: Mon, 13 Jan 2014 12:56:21 -0500
Subject: [PATCH] ftrace: Fix synchronization location disabling and freeing
ftrace_ops
The synchronization needed after ftrace_ops are unregistered must happen
after the callback is disabled from becing called by functions.
The current location happens after the function is being removed from the
internal lists, but not after the function callbacks were disabled, leaving
the functions susceptible of being called after their callbacks are freed.
This affects perf and any externel users of function tracing (LTTng and
SystemTap).
Cc: stable@xxxxxxxxxxxxxxx # 3.0+
Fixes: cdbe61bfe704 "ftrace: Allow dynamically allocated function tracers"
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 7f21b06648e9..7181ad15923b 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -498,20 +498,6 @@ static int __unregister_ftrace_function(struct ftrace_ops *ops)
} else if (ops->flags & FTRACE_OPS_FL_CONTROL) {
ret = remove_ftrace_list_ops(&ftrace_control_list,
&control_ops, ops);
- if (!ret) {
- /*
- * The ftrace_ops is now removed from the list,
- * so there'll be no new users. We must ensure
- * all current users are done before we free
- * the control data.
- * Note synchronize_sched() is not enough, as we
- * use preempt_disable() to do RCU, but the function
- * tracer can be called where RCU is not active
- * (before user_exit()).
- */
- schedule_on_each_cpu(ftrace_sync);
- control_ops_free(ops);
- }
} else
ret = remove_ftrace_ops(&ftrace_ops_list, ops);
@@ -521,17 +507,6 @@ static int __unregister_ftrace_function(struct ftrace_ops *ops)
if (ftrace_enabled)
update_ftrace_function();
- /*
- * Dynamic ops may be freed, we must make sure that all
- * callers are done before leaving this function.
- *
- * Again, normal synchronize_sched() is not good enough.
- * We need to do a hard force of sched synchronization.
- */
- if (ops->flags & FTRACE_OPS_FL_DYNAMIC)
- schedule_on_each_cpu(ftrace_sync);
-
-
return 0;
}
@@ -2208,10 +2183,41 @@ static int ftrace_shutdown(struct ftrace_ops *ops, int command)
command |= FTRACE_UPDATE_TRACE_FUNC;
}
- if (!command || !ftrace_enabled)
+ if (!command || !ftrace_enabled) {
+ /*
+ * If these are control ops, they still need their
+ * per_cpu field freed. Since, function tracing is
+ * not currently active, we can just free them
+ * without synchronizing all CPUs.
+ */
+ if (ops->flags & FTRACE_OPS_FL_CONTROL)
+ control_ops_free(ops);
return 0;
+ }
ftrace_run_update_code(command);
+
+ /*
+ * Dynamic ops may be freed, we must make sure that all
+ * callers are done before leaving this function.
+ * The same goes for freeing the per_cpu data of the control
+ * ops.
+ *
+ * Again, normal synchronize_sched() is not good enough.
+ * We need to do a hard force of sched synchronization.
+ * This is because we use preempt_disable() to do RCU, but
+ * the function tracers can be called where RCU is not watching
+ * (like before user_exit()). We can not rely on the RCU
+ * infrastructure to do the synchronization, thus we must do it
+ * ourselves.
+ */
+ if (ops->flags & (FTRACE_OPS_FL_DYNAMIC | FTRACE_OPS_FL_CONTROL)) {
+ schedule_on_each_cpu(ftrace_sync);
+
+ if (ops->flags & FTRACE_OPS_FL_CONTROL)
+ control_ops_free(ops);
+ }
+
return 0;
}
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