Re: [PATCH v2] perf/ftrace: Fix WARNING in __unregister_ftrace_function
From: Rik van Riel
Date: Wed May 13 2026 - 13:25:38 EST
On Wed, 13 May 2026 12:33:44 -0400
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> Instead of duplicating code, what about doing:
That is much nicer. Thank you!
---8<---
From 9de86227b917c49315b7b67aac3a83afae8d792d Mon Sep 17 00:00:00 2001
From: Rik van Riel <riel@xxxxxxxx>
Date: Sat, 25 Apr 2026 03:33:54 -0700
Subject: [PATCH] perf/ftrace: Fix WARNING in __unregister_ftrace_function
perf_ftrace_function_unregister() unconditionally calls
unregister_ftrace_function() without checking whether the ftrace_ops
was ever successfully registered. This triggers a WARN_ON in
__unregister_ftrace_function() when the ops doesn't have
FTRACE_OPS_FL_ENABLED set.
This can happen during perf_event_alloc() error cleanup when
perf_trace_destroy() is called via __free_event() on an event whose
ftrace_ops registration failed or was already torn down by
perf_try_init_event()'s err_destroy path.
The call path is:
perf_event_alloc() error cleanup
-> __free_event()
-> event->destroy() [tp_perf_event_destroy]
-> perf_trace_destroy()
-> perf_trace_event_close()
-> TRACE_REG_PERF_CLOSE
-> perf_ftrace_function_unregister()
-> unregister_ftrace_function()
-> __unregister_ftrace_function()
-> WARN_ON(!(ops->flags & FTRACE_OPS_FL_ENABLED))
Fix this by checking FTRACE_OPS_FL_ENABLED before attempting to
unregister. If the ops is not enabled, just free the filter and
return success.
Assisted-by: Claude:claude-opus-4.7 syzkaller
Signed-off-by: Rik van Riel <riel@xxxxxxxxxxx>
---
kernel/trace/trace_event_perf.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index a6bb7577e8c5..58e1b427b576 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -497,7 +497,11 @@ static int perf_ftrace_function_register(struct perf_event *event)
static int perf_ftrace_function_unregister(struct perf_event *event)
{
struct ftrace_ops *ops = &event->ftrace_ops;
- int ret = unregister_ftrace_function(ops);
+ int ret = 0;
+
+ if (ops->flags & FTRACE_OPS_FL_ENABLED)
+ ret = unregister_ftrace_function(ops);
+
ftrace_free_filter(ops);
return ret;
}
--
2.52.0