linux-kernel - Re: [PATCH 3/3] tracing: Check cpu file on tracing

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Date:	Wed, 10 Apr 2013 10:30:07 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Namhyung Kim <namhyung.kim@....com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] tracing: Check cpu file on tracing_release()

On Tue, 09 Apr 2013 20:46:27 -0400, Steven Rostedt wrote:
> On Wed, 2013-04-10 at 09:36 +0900, Namhyung Kim wrote:
>
>> You meant iter->cpu_file != RING_BUFFER_ALL_CPUS case, right?
>
> Yep.
>
>> 
>> So why bother trying to check other cpus then?
>
> Because it's a very slow path (closing a file), and it keeps the code
> simpler and more condense.
>
> We could add your change for consistency, but right now, its very low
> priority.

Hmm.. okay.

>
> But looking at the code, I do see a clean up that looks like it would be
> worth updating. If the ring_buffer_read_prepare() fails, we should
> probably let the user know, instead of succeeding and then having no
> output.

How about below.. :)


>From 7ba245dba217ef858b467552019acd49f7fdce7e Mon Sep 17 00:00:00 2001
From: Namhyung Kim <namhyung.kim@....com>
Date: Wed, 10 Apr 2013 09:10:44 +0900
Subject: [PATCH] tracing: Check result of ring_buffer_read_prepare()

The ring_buffer_read_prepare() can return NULL if memory allocation
fails.  Fail out in this case instead of succedding and then having
no output.

Suggested-by: Steven Rostedt <rostedt@...dmis.org>
Signed-off-by: Namhyung Kim <namhyung@...nel.org>
---
 kernel/trace/trace.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 7270460cfe3c..3b3514dc8e5e 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2826,6 +2826,8 @@ __tracing_open(struct inode *inode, struct file *file, bool snapshot)
 		for_each_tracing_cpu(cpu) {
 			iter->buffer_iter[cpu] =
 				ring_buffer_read_prepare(iter->trace_buffer->buffer, cpu);
+			if (!iter->buffer_iter[cpu])
+				goto free;
 		}
 		ring_buffer_read_prepare_sync();
 		for_each_tracing_cpu(cpu) {
@@ -2836,6 +2838,9 @@ __tracing_open(struct inode *inode, struct file *file, bool snapshot)
 		cpu = iter->cpu_file;
 		iter->buffer_iter[cpu] =
 			ring_buffer_read_prepare(iter->trace_buffer->buffer, cpu);
+		if (!iter->buffer_iter[cpu])
+			goto free;
+
 		ring_buffer_read_prepare_sync();
 		ring_buffer_read_start(iter->buffer_iter[cpu]);
 		tracing_iter_reset(iter, cpu);
@@ -2847,6 +2852,26 @@ __tracing_open(struct inode *inode, struct file *file, bool snapshot)
 
 	return iter;
 
+free:
+	if (iter->cpu_file == RING_BUFFER_ALL_CPUS) {
+		for_each_tracing_cpu(cpu) {
+			if (iter->buffer_iter[cpu])
+				ring_buffer_read_finish(iter->buffer_iter[cpu]);
+		}
+	} else {
+		cpu = iter->cpu_file;
+		if (iter->buffer_iter[cpu])
+			ring_buffer_read_finish(iter->buffer_iter[cpu]);
+	}
+
+	if (iter->trace && iter->trace->close)
+		iter->trace->close(iter);
+
+	if (!iter->snapshot)
+		tracing_start_tr(tr);
+
+	mutex_destroy(&iter->mutex);
+	free_cpumask_var(iter->started);
  fail:
 	mutex_unlock(&trace_types_lock);
 	kfree(iter->trace);
-- 
1.7.11.7

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