Re: [PATCH] trace: Fix some checker warnings

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Mon, 05 Dec 2022 08:28:35 +0000
David Howells <dhowells@redhat.com> wrote:

> Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:
> 
> > > +#if defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER)
> > >  static const struct file_operations tracing_max_lat_fops;
> > > +#endif
> > 
> > Oops, I missed this part. Why did you introduced this #ifdefs?
> 
> Because:
> 
>     #if defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER)
>     static const struct file_operations tracing_max_lat_fops = {
> 
> in the same file.  You get something like an unused symbol warning otherwise
> if neither config option is defined.

Yeah, I got it. Without the above change, the compile error will be gone,
but this means that the declaration becomes a definition. (it uses an empty
data structure)

Could you remove that part from your printf checker macro, and
apply the below patch?
Since the printf macros are a kind of improvement but this part is an
actual bug, need to be fixed on stable kernel too.


From 2e993ec80d864677fd42d27f9d4ee01d7e63f8a4 Mon Sep 17 00:00:00 2001
From: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Date: Mon, 5 Dec 2022 14:27:00 +0900
Subject: [PATCH] tracing: Fix complicated dependency of
 CONFIG_TRACER_MAX_TRACE

Both CONFIG_OSNOISE_TRACER and CONFIG_HWLAT_TRACER partially enables the
CONFIG_TRACER_MAX_TRACE code, but that is complicated and has
introduced a bug; It declares tracing_max_lat_fops data structure outside
of #ifdefs, but since it is defined only when CONFIG_TRACER_MAX_TRACE=y
or CONFIG_HWLAT_TRACER=y, if only CONFIG_OSNOISE_TRACER=y, that
declaration comes to a definition(!).

To fix this issue, and do not repeat the similar problem, makes
CONFIG_OSNOISE_TRACER and CONFIG_HWLAT_TRACER enables the
CONFIG_TRACER_MAX_TRACE always. It has there benefits;
- Fix the tracing_max_lat_fops bug
- Simplify the #ifdefs
- CONFIG_TRACER_MAX_TRACE code is fully enabled, or not.

Fixes: 424b650f35c7 ("tracing: Fix missing osnoise tracer on max_latency")
Cc: stable@vger.kernel.org
Reported-by: David Howells <dhowells@redhat.com>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 kernel/trace/Kconfig |  2 ++
 kernel/trace/trace.c | 15 ++++++++-------
 kernel/trace/trace.h |  8 +++-----
 3 files changed, 13 insertions(+), 12 deletions(-)

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index e9e95c790b8e..93d724996283 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -375,6 +375,7 @@ config SCHED_TRACER
 config HWLAT_TRACER
 	bool "Tracer to detect hardware latencies (like SMIs)"
 	select GENERIC_TRACER
+	select TRACER_MAX_TRACE
 	help
 	 This tracer, when enabled will create one or more kernel threads,
 	 depending on what the cpumask file is set to, which each thread
@@ -410,6 +411,7 @@ config HWLAT_TRACER
 config OSNOISE_TRACER
 	bool "OS Noise tracer"
 	select GENERIC_TRACER
+	select TRACER_MAX_TRACE
 	help
 	  In the context of high-performance computing (HPC), the Operating
 	  System Noise (osnoise) refers to the interference experienced by an
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 5cfc95a52bc3..08033347df2c 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1692,6 +1692,8 @@ static ssize_t trace_seq_to_buffer(struct trace_seq *s, void *buf, size_t cnt)
 }
 
 unsigned long __read_mostly	tracing_thresh;
+
+#ifdef CONFIG_TRACER_MAX_TRACE
 static const struct file_operations tracing_max_lat_fops;
 
 #ifdef LATENCY_FS_NOTIFY
@@ -1748,18 +1750,14 @@ void latency_fsnotify(struct trace_array *tr)
 	irq_work_queue(&tr->fsnotify_irqwork);
 }
 
-#elif defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER)	\
-	|| defined(CONFIG_OSNOISE_TRACER)
+#else /* !LATENCY_FS_NOTIFY */
 
 #define trace_create_maxlat_file(tr, d_tracer)				\
 	trace_create_file("tracing_max_latency", TRACE_MODE_WRITE,	\
 			  d_tracer, &tr->max_latency, &tracing_max_lat_fops)
 
-#else
-#define trace_create_maxlat_file(tr, d_tracer)	 do { } while (0)
 #endif
 
-#ifdef CONFIG_TRACER_MAX_TRACE
 /*
  * Copy the new maximum trace into the separate maximum-trace
  * structure. (this way the maximum trace is permanently saved,
@@ -1888,6 +1886,7 @@ update_max_tr_single(struct trace_array *tr, struct task_struct *tsk, int cpu)
 	__update_max_tr(tr, tsk, cpu);
 	arch_spin_unlock(&tr->max_lock);
 }
+
 #endif /* CONFIG_TRACER_MAX_TRACE */
 
 static int wait_on_pipe(struct trace_iterator *iter, int full)
@@ -6572,7 +6571,7 @@ tracing_thresh_write(struct file *filp, const char __user *ubuf,
 	return ret;
 }
 
-#if defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER)
+#ifdef CONFIG_TRACER_MAX_TRACE
 
 static ssize_t
 tracing_max_lat_read(struct file *filp, char __user *ubuf,
@@ -7587,7 +7586,7 @@ static const struct file_operations tracing_thresh_fops = {
 	.llseek		= generic_file_llseek,
 };
 
-#if defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER)
+#ifdef CONFIG_TRACER_MAX_TRACE
 static const struct file_operations tracing_max_lat_fops = {
 	.open		= tracing_open_generic,
 	.read		= tracing_max_lat_read,
@@ -9601,7 +9600,9 @@ init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer)
 
 	create_trace_options_dir(tr);
 
+#ifdef CONFIG_TRACER_MAX_TRACE
 	trace_create_maxlat_file(tr, d_tracer);
+#endif
 
 	if (ftrace_create_function_files(tr, d_tracer))
 		MEM_FAIL(1, "Could not allocate function filter files");
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index d42e24507152..8b69698780a1 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -308,8 +308,7 @@ struct trace_array {
 	struct array_buffer	max_buffer;
 	bool			allocated_snapshot;
 #endif
-#if defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER) \
-	|| defined(CONFIG_OSNOISE_TRACER)
+#ifdef CONFIG_TRACER_MAX_TRACE
 	unsigned long		max_latency;
 #ifdef CONFIG_FSNOTIFY
 	struct dentry		*d_max_latency;
@@ -688,12 +687,11 @@ void update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu,
 		   void *cond_data);
 void update_max_tr_single(struct trace_array *tr,
 			  struct task_struct *tsk, int cpu);
-#endif /* CONFIG_TRACER_MAX_TRACE */
 
-#if (defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER) \
-	|| defined(CONFIG_OSNOISE_TRACER)) && defined(CONFIG_FSNOTIFY)
+#ifdef CONFIG_FSNOTIFY
 #define LATENCY_FS_NOTIFY
 #endif
+#endif /* CONFIG_TRACER_MAX_TRACE */
 
 #ifdef LATENCY_FS_NOTIFY
 void latency_fsnotify(struct trace_array *tr);
-- 
2.39.0.rc0.267.gcb52ba06e7-goog

-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>