[PATCH 06/15] ftrace: enable filtering only when a function is filtered on

Steven Rostedt
2009-02-17T05:15:36Z

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From: Steven Rostedt <srostedt@redhat.com>

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>
---
kernel/trace/ftrace.c | 14 ++++++++------
1 files changed, 8 insertions(+), 6 deletions(-)

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 @@ static void ftrace_match_records(char *buff, int len, int enable)

/* 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 @@ static void ftrace_match_records(char *buff, int len, int enable)
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 @@ static void ftrace_match_module_records(char *buff, char *mod, int enable)

/* 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 @@ static void ftrace_match_module_records(char *buff, char *mod, int enable)
else
rec->flags |= flag;
}
+ if (enable && (rec->flags & FTRACE_FL_FILTER))
+ ftrace_filtered = 1;

} while_for_each_ftrace_rec();
spin_unlock(&ftrace_lock);
--
1.5.6.5

--