Commit 57b76bed authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Steven Rostedt (Google)
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ftrace: Correct preemption accounting for function tracing. 

The function tracer should record the preemption level at the point when
the function is invoked. If the tracing subsystem decrement the
preemption counter it needs to correct this before feeding the data into
the trace buffer. This was broken in the commit cited below while
shifting the preempt-disabled section.

Use tracing_gen_ctx_dec() which properly subtracts one from the
preemption counter on a preemptible kernel.

Cc: stable@vger.kernel.org
Cc: Wander Lairson Costa <wander@redhat.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/20250220140749.pfw8qoNZ@linutronix.de


Fixes: ce5e4803 ("ftrace: disable preemption when recursion locked")
Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: default avatarWander Lairson Costa <wander@redhat.com>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent e85c5e97

kernel/trace/trace_functions.c

+2 −4
Original line number Diff line number Diff line
@@ -216,7 +216,7 @@ function_trace_call(unsigned long ip, unsigned long parent_ip, 


	parent_ip = function_get_true_parent_ip(parent_ip, fregs);



	trace_ctx = tracing_gen_ctx();

	trace_ctx = tracing_gen_ctx_dec();



	data = this_cpu_ptr(tr->array_buffer.data);

	if (!atomic_read(&data->disabled))
@@ -321,7 +321,6 @@ function_no_repeats_trace_call(unsigned long ip, unsigned long parent_ip, 
	struct trace_array *tr = op->private;

	struct trace_array_cpu *data;

	unsigned int trace_ctx;

	unsigned long flags;

	int bit;



	if (unlikely(!tr->function_enabled))
@@ -347,8 +346,7 @@ function_no_repeats_trace_call(unsigned long ip, unsigned long parent_ip, 
	if (is_repeat_check(tr, last_info, ip, parent_ip))

		goto out;



	local_save_flags(flags);

	trace_ctx = tracing_gen_ctx_flags(flags);

	trace_ctx = tracing_gen_ctx_dec();

	process_repeats(tr, ip, parent_ip, last_info, trace_ctx);



	trace_function(tr, ip, parent_ip, trace_ctx);