Commit cc337974 authored Mar 02, 2026 by Steven Rostedt Committed by Steven Rostedt (Google) Mar 03, 2026

ftrace: Disable preemption in the tracepoint callbacks handling filtered pids

When function trace PID filtering is enabled, the function tracer will
attach a callback to the fork tracepoint as well as the exit tracepoint
that will add the forked child PID to the PID filtering list as well as
remove the PID that is exiting.

Commit a46023d5 ("tracing: Guard __DECLARE_TRACE() use of
__DO_TRACE_CALL() with SRCU-fast") removed the disabling of preemption
when calling tracepoint callbacks.

The callbacks used for the PID filtering accounting depended on preemption
being disabled, and now the trigger a "suspicious RCU usage" warning message.

Make them explicitly disable preemption.

Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://patch.msgid.link/20260302213546.156e3e4f@gandalf.local.home


Fixes: a46023d5 ("tracing: Guard __DECLARE_TRACE() use of __DO_TRACE_CALL() with SRCU-fast")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

parent 0a663b76

kernel/trace/ftrace.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -8611,6 +8611,7 @@ ftrace_pid_follow_sched_process_fork(void *data,
		struct trace_pid_list *pid_list;
		struct trace_array *tr = data;

		guard(preempt)();
		pid_list = rcu_dereference_sched(tr->function_pids);
		trace_filter_add_remove_task(pid_list, self, task);

		@@ -8624,6 +8625,7 @@ ftrace_pid_follow_sched_process_exit(void data, struct task_struct task)
		struct trace_pid_list *pid_list;
		struct trace_array *tr = data;

		guard(preempt)();
		pid_list = rcu_dereference_sched(tr->function_pids);
		trace_filter_add_remove_task(pid_list, NULL, task);