ftrace: Only update the function code on write to filter files

BugLink: http://bugs.launchpad.net/bugs/793702

commit 058e297d34a404caaa5ed277de15698d8dc43000 upstream.

If function tracing is enabled, a read of the filter files will
cause the call to stop_machine to update the function trace sites.
It should only call stop_machine on write.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 888b611..9803b68 100644 (file)
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2414,14 +2414,16 @@ ftrace_regex_release(struct inode *inode, struct file *file, int enable)
                ftrace_match_records(parser->buffer, parser->idx, enable);
        }
 
-       mutex_lock(&ftrace_lock);
-       if (ftrace_start_up && ftrace_enabled)
-               ftrace_run_update_code(FTRACE_ENABLE_CALLS);
-       mutex_unlock(&ftrace_lock);
-
        trace_parser_put(parser);
        kfree(iter);
 
+       if (file->f_mode & FMODE_WRITE) {
+               mutex_lock(&ftrace_lock);
+               if (ftrace_start_up && ftrace_enabled)
+                       ftrace_run_update_code(FTRACE_ENABLE_CALLS);
+               mutex_unlock(&ftrace_lock);
+       }
+
        mutex_unlock(&ftrace_regex_lock);
        return 0;
 }