From: Steven Rostedt <rostedt@goodmis.org>
Date: Mon, 5 May 2025 21:21:16 +0000 (-0400)
Subject: tracing: Use atomic_inc_return() for updating "disabled" counter in irqsoff tracer
X-Git-Tag: v6.16-rc1~121^2~12
X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=c4a80c06154084d52851fe495d40b0e4da032f47;p=linux-block.git

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: Steven Rostedt (Google) <rostedt@goodmis.org>
---

diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
index 0b6d932a931e..5496758b6c76 100644
--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -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;
@@ -411,15 +412,17 @@ 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);
 
-	data->critical_sequence = max_sequence;
-	data->preempt_timestamp = ftrace_now(cpu);
-	data->critical_start = parent_ip ? : ip;
+	if (disabled == 1) {
+		data->critical_sequence = max_sequence;
+		data->preempt_timestamp = ftrace_now(cpu);
+		data->critical_start = parent_ip ? : ip;
 
-	__trace_function(tr, ip, parent_ip, tracing_gen_ctx());
+		__trace_function(tr, ip, parent_ip, tracing_gen_ctx());
 
-	per_cpu(tracing_cpu, cpu) = 1;
+		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;
+	}
 
-	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);
 }