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fprobe: Always unregister fgraph function from ops

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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@vger.kernel.org
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Link: https://lore.kernel.org/20250220202055.393254452@goodmis.org
Fixes: 4346ba1604 ("fprobe: Rewrite fprobe on function-graph tracer")
Tested-by: Heiko Carstens <hca@linux.ibm.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt 2025-02-20 15:20:12 -05:00 • committed by Steven Rostedt (Google)
parent 8eb4b09e0b
commit ded9140622
1 changed files with 2 additions and 4 deletions
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6
kernel/trace/fprobe.c
View file

@ -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);
}