Commit c4a80c06 authored by Steven Rostedt's avatar Steven Rostedt Committed by Steven Rostedt (Google)
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tracing: Use atomic_inc_return() for updating "disabled" counter in irqsoff tracer 

The irqsoff tracer uses the per CPU "disabled" field to prevent corruption
of the accounting when it starts to trace interrupts disabled, but there's
a slight race that could happen if for some reason it was called twice.
Use atomic_inc_return() instead.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: https://lore.kernel.org/20250505212236.567884756@goodmis.org


Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent 90633c34

kernel/trace/trace_irqsoff.c

+18 −11
Original line number Diff line number Diff line
@@ -397,6 +397,7 @@ start_critical_timing(unsigned long ip, unsigned long parent_ip) 
	int cpu;

	struct trace_array *tr = irqsoff_trace;

	struct trace_array_cpu *data;

	long disabled;



	if (!tracer_enabled || !tracing_is_enabled())

		return;
@@ -411,8 +412,9 @@ start_critical_timing(unsigned long ip, unsigned long parent_ip) 
	if (unlikely(!data) || local_read(&data->disabled))

		return;



	local_inc(&data->disabled);

	disabled = local_inc_return(&data->disabled);



	if (disabled == 1) {

		data->critical_sequence = max_sequence;

		data->preempt_timestamp = ftrace_now(cpu);

		data->critical_start = parent_ip ? : ip;
@@ -420,6 +422,7 @@ start_critical_timing(unsigned long ip, unsigned long parent_ip) 
		__trace_function(tr, ip, parent_ip, tracing_gen_ctx());



		per_cpu(tracing_cpu, cpu) = 1;

	}



	local_dec(&data->disabled);

}
@@ -431,6 +434,7 @@ stop_critical_timing(unsigned long ip, unsigned long parent_ip) 
	struct trace_array *tr = irqsoff_trace;

	struct trace_array_cpu *data;

	unsigned int trace_ctx;

	long disabled;



	cpu = raw_smp_processor_id();

	/* Always clear the tracing cpu on stopping the trace */
@@ -448,12 +452,15 @@ stop_critical_timing(unsigned long ip, unsigned long parent_ip) 
	    !data->critical_start || local_read(&data->disabled))

		return;



	local_inc(&data->disabled);

	disabled = local_inc_return(&data->disabled);



	if (disabled == 1) {

		trace_ctx = tracing_gen_ctx();

		__trace_function(tr, ip, parent_ip, trace_ctx);

		check_critical_timing(tr, data, parent_ip ? : ip, cpu);

		data->critical_start = 0;

	}



	local_dec(&data->disabled);

}