linux-kernel - Re: [PATCH 4/7 v2] tracing: Have trace events system open call tracing_open_generic

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Message-ID: <20191011220940.3aeee7a5@oasis.local.home>
Date:   Fri, 11 Oct 2019 22:09:40 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Garrett <matthewgarrett@...gle.com>,
        James Morris James Morris <jmorris@...ei.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Ben Hutchings <ben@...adent.org.uk>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 4/7 v2] tracing: Have trace events system open call
 tracing_open_generic_tr()

On Fri, 11 Oct 2019 20:57:51 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -1391,9 +1391,6 @@ static int subsystem_open(struct inode *inode, struct file *filp)
>  	struct trace_array *tr;
>  	int ret;
>  
> -	if (tracing_is_disabled())
> -		return -ENODEV;
> -
>  	/* Make sure the system still exists */
>  	mutex_lock(&event_mutex);
>  	mutex_lock(&trace_types_lock);
> @@ -1420,16 +1417,9 @@ static int subsystem_open(struct inode *inode, struct file *filp)
>  	WARN_ON(!dir);
>  
>  	/* Still need to increment the ref count of the system */
> -	if (trace_array_get(tr) < 0) {
> -		put_system(dir);
> -		return -ENODEV;
> -	}
> -
> -	ret = tracing_open_generic(inode, filp);
> -	if (ret < 0) {
> -		trace_array_put(tr);
> +	ret = tracing_open_generic_tr(inode, filp);
> +	if (ret < 0)
>  		put_system(dir);
> -	}
>  
>  	return ret;
>  }

I got a bit too aggressive on this patch. The subsystem_open() gets the
tr from a search, not from the inode. Thus it can't use the
tracing_open_generic_tr() call. It needs to do the trace_array_get()
directly.

V2 of this patch:

-- Steve

>From b69083301044f587afefd5a4ac754a8c43ba0f0d Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
Date: Fri, 11 Oct 2019 19:12:21 -0400
Subject: [PATCH] tracing: Have trace events system open call
 tracing_open_generic_tr()

Instead of having the trace events system open calls open code the taking of
the trace_array descriptor (with trace_array_get()) and then calling
trace_open_generic(), have it use the tracing_open_generic_tr() that does
the combination of the two. This requires making tracing_open_generic_tr()
global.

Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 kernel/trace/trace.c        |  2 +-
 kernel/trace/trace.h        |  1 +
 kernel/trace/trace_events.c | 17 +++--------------
 3 files changed, 5 insertions(+), 15 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index fa7d813b04c6..94f1b9124939 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4156,7 +4156,7 @@ bool tracing_is_disabled(void)
  * Open and update trace_array ref count.
  * Must have the current trace_array passed to it.
  */
-static int tracing_open_generic_tr(struct inode *inode, struct file *filp)
+int tracing_open_generic_tr(struct inode *inode, struct file *filp)
 {
 	struct trace_array *tr = inode->i_private;
 
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index f801d154ff6a..854dbf4050f8 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -681,6 +681,7 @@ void tracing_reset_online_cpus(struct trace_buffer *buf);
 void tracing_reset_current(int cpu);
 void tracing_reset_all_online_cpus(void);
 int tracing_open_generic(struct inode *inode, struct file *filp);
+int tracing_open_generic_tr(struct inode *inode, struct file *filp);
 bool tracing_is_disabled(void);
 bool tracer_tracing_is_on(struct trace_array *tr);
 void tracer_tracing_on(struct trace_array *tr);
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index b89cdfe20bc1..9613a757c902 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1440,28 +1440,17 @@ static int system_tr_open(struct inode *inode, struct file *filp)
 	struct trace_array *tr = inode->i_private;
 	int ret;
 
-	if (tracing_is_disabled())
-		return -ENODEV;
-
-	if (trace_array_get(tr) < 0)
-		return -ENODEV;
-
 	/* Make a temporary dir that has no system but points to tr */
 	dir = kzalloc(sizeof(*dir), GFP_KERNEL);
-	if (!dir) {
-		trace_array_put(tr);
+	if (!dir)
 		return -ENOMEM;
-	}
-
-	dir->tr = tr;
 
-	ret = tracing_open_generic(inode, filp);
+	ret = tracing_open_generic_tr(inode, filp);
 	if (ret < 0) {
-		trace_array_put(tr);
 		kfree(dir);
 		return ret;
 	}
-
+	dir->tr = tr;
 	filp->private_data = dir;
 
 	return 0;
-- 
2.20.1