ftrace: enable filtering only when a function is filtered on
Impact: fix to prevent empty set_ftrace_filter and no ftrace output
The function filter is used to only trace a given set of functions.
The filter is enabled when a function name is echoed into the
set_ftrace_filter file. But if the name has a typo and the function
is not found, the filter is enabled, but no function is listed.
This makes a confusing situation where set_ftrace_filter is empty
but no functions ever get enabled for tracing.
For example:
# cat /debug/tracing/set_ftrace_filter
#### all functions enabled ####
# echo bad_name > set_ftrace_filter
# cat /debug/tracing/set_ftrace_filter
# echo function > current_tracer
# cat trace
# tracer: nop
#
# TASK-PID CPU# TIMESTAMP FUNCTION
# | | | | |
This patch changes that to only enable filtering if a function
is set to be filtered on. Now, the filter is not enabled if
a bad name is echoed into set_ftrace_filter.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 9e60ae4..340f88b 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1153,8 +1153,6 @@
/* should not be called from interrupt context */
spin_lock(&ftrace_lock);
- if (enable)
- ftrace_filtered = 1;
do_for_each_ftrace_rec(pg, rec) {
if (rec->flags & FTRACE_FL_FAILED)
@@ -1166,7 +1164,12 @@
else
rec->flags |= flag;
}
-
+ /*
+ * Only enable filtering if we have a function that
+ * is filtered on.
+ */
+ if (enable && (rec->flags & FTRACE_FL_FILTER))
+ ftrace_filtered = 1;
} while_for_each_ftrace_rec();
spin_unlock(&ftrace_lock);
}
@@ -1217,9 +1220,6 @@
/* should not be called from interrupt context */
spin_lock(&ftrace_lock);
- if (enable)
- ftrace_filtered = 1;
-
do_for_each_ftrace_rec(pg, rec) {
if (rec->flags & FTRACE_FL_FAILED)
@@ -1232,6 +1232,8 @@
else
rec->flags |= flag;
}
+ if (enable && (rec->flags & FTRACE_FL_FILTER))
+ ftrace_filtered = 1;
} while_for_each_ftrace_rec();
spin_unlock(&ftrace_lock);