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List:       linux-kernel
Subject:    [for-next][PATCH 2/5] trace/osnoise: Make noise variable s64 in run_osnoise()
From:       Steven Rostedt <rostedt () goodmis ! org>
Date:       2021-06-30 23:18:00
Message-ID: 20210630231822.219090027 () goodmis ! org
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From: Daniel Bristot de Oliveira <bristot@redhat.com>

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.

Link: https://lkml.kernel.org/r/acd7cd6e7d56b798a298c3bc8139a390b3c4ab52.1624986368.git.bristot@redhat.com


Cc: Ingo Molnar <mingo@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: linux-kernel@vger.kernel.org
Fixes: bce29ac9ce0b ("trace: Add osnoise tracer")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 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;
 
 	/*
-- 
2.30.2


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