From: Steven Rostedt <rostedt@xxxxxxxxxxx>
When the last fprobe is removed, it calls unregister_ftrace_graph() to
remove the graph_ops from function graph. The issue is when it does so, it
calls return before removing the function from its graph ops via
ftrace_set_filter_ips(). This leaves the last function lingering in the
fprobe's fgraph ops and if a probe is added it also enables that last
function (even though the callback will just drop it, it does add unneeded
overhead to make that call).
# echo "f:myevent1 kernel_clone" >> /sys/kernel/tracing/dynamic_events
# cat /sys/kernel/tracing/enabled_functions
kernel_clone (1) tramp: 0xffffffffc02f3000 (ftrace_graph_func+0x0/0x60) ->ftrace_graph_func+0x0/0x60
# echo "f:myevent2 schedule_timeout" >> /sys/kernel/tracing/dynamic_events
# cat /sys/kernel/tracing/enabled_functions
kernel_clone (1) tramp: 0xffffffffc02f3000 (ftrace_graph_func+0x0/0x60) ->ftrace_graph_func+0x0/0x60
schedule_timeout (1) tramp: 0xffffffffc02f3000 (ftrace_graph_func+0x0/0x60) ->ftrace_graph_func+0x0/0x60
# > /sys/kernel/tracing/dynamic_events
# cat /sys/kernel/tracing/enabled_functions
# echo "f:myevent3 kmem_cache_free" >> /sys/kernel/tracing/dynamic_events
# cat /sys/kernel/tracing/enabled_functions
kmem_cache_free (1) tramp: 0xffffffffc0219000 (ftrace_graph_func+0x0/0x60) ->ftrace_graph_func+0x0/0x60
schedule_timeout (1) tramp: 0xffffffffc0219000 (ftrace_graph_func+0x0/0x60) ->ftrace_graph_func+0x0/0x60
The above enabled a fprobe on kernel_clone, and then on schedule_timeout.
The content of the enabled_functions shows the functions that have a
callback attached to them. The fprobe attached to those functions
properly. Then the fprobes were cleared, and enabled_functions was empty
after that. But after adding a fprobe on kmem_cache_free, the
enabled_functions shows that the schedule_timeout was attached again. This
is because it was still left in the fprobe ops that is used to tell
function graph what functions it wants callbacks from.
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 4346ba1604093 ("fprobe: Rewrite fprobe on function-graph tracer")
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
---
kernel/trace/fprobe.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
index 2560b312ad57..62e8f7d56602 100644
--- a/kernel/trace/fprobe.c
+++ b/kernel/trace/fprobe.c
@@ -403,11 +403,9 @@ static void fprobe_graph_remove_ips(unsigned long *addrs, int num)
lockdep_assert_held(&fprobe_mutex);
fprobe_graph_active--;
- if (!fprobe_graph_active) {
- /* Q: should we unregister it ? */
+ /* Q: should we unregister it ? */
+ if (!fprobe_graph_active)
unregister_ftrace_graph(&fprobe_graph_ops);
- return;
- }
ftrace_set_filter_ips(&fprobe_graph_ops.ops, addrs, num, 1, 0);
}
--
2.47.2
