linux-kernel - [PATCH 1/2] trace/osnoise: Make 'noise' variable s64 in run

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Date:   Tue, 29 Jun 2021 19:10:26 +0200
From:   Daniel Bristot de Oliveira <bristot@...hat.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Daniel Bristot de Oliveira <bristot@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] trace/osnoise: Make 'noise' variable s64 in run_osnoise()

Dab Carpenter reported that:

 The patch bce29ac9ce0b: "trace: Add osnoise tracer" from Jun 22,
 2021, leads to the following static checker warning:

	kernel/trace/trace_osnoise.c:1103 run_osnoise()
	warn: unsigned 'noise' is never less than zero.

In this part of the code:

  1100                  /*
  1101                   * This shouldn't happen.
  1102                   */
  1103                  if (noise < 0) {
                            ^^^^^^^^^
  1104                          osnoise_taint("negative noise!");
  1105                          goto out;
  1106                  }
  1107

And the static checker is right because 'noise' is u64.

Make noise s64 and keep the check. It is important to check if
the time read is behaving correctly - so we can trust the results.

I also re-arranged some variable declarations.

Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
Cc: Dan Carpenter <dan.carpenter@...cle.com>
Cc: linux-kernel@...r.kernel.org
Fixes: bce29ac9ce0b ("trace: Add osnoise tracer")
Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Daniel Bristot de Oliveira <bristot@...hat.com>
---
 kernel/trace/trace_osnoise.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 085a83de98ad..cc1faca1a620 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -1042,15 +1042,16 @@ static void osnoise_stop_tracing(void)
 static int run_osnoise(void)
 {
 	struct osnoise_variables *osn_var = this_cpu_osn_var();
-	u64 noise = 0, sum_noise = 0, max_noise = 0;
 	struct trace_array *tr = osnoise_trace;
 	u64 start, sample, last_sample;
 	u64 last_int_count, int_count;
+	s64 noise = 0, max_noise = 0;
 	s64 total, last_total = 0;
 	struct osnoise_sample s;
 	unsigned int threshold;
-	int hw_count = 0;
 	u64 runtime, stop_in;
+	u64 sum_noise = 0;
+	int hw_count = 0;
 	int ret = -1;
 
 	/*
-- 
2.31.1