linux-kernel - Re: [PATCH v2 2/2] tracing: Add free_trace_iter

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Date:   Fri, 28 Jul 2023 19:08:19 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 2/2] tracing: Add free_trace_iter_content() helper
 function

On Wed, 26 Jul 2023 22:42:13 +0900
Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:

> On Sat, 15 Jul 2023 10:12:15 -0400
> Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > From: "Steven Rostedt (Google)" <rostedt@...dmis.org>
> > 
> > As the trace iterator is created and used by various interfaces, the clean
> > up of it needs to be consistent. Create a free_trace_iter_content() helper
> > function that frees the content of the iterator and use that to clean it
> > up in all places that it is used.
> > 
> > Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>  
> 
> Looks good to me.
> 
> Reviewed-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> 
> BTW, this adds iter->fmt != static_fmt_buf check. Is it a kind of fix?

No, because all of the callers shouldn't actually set it to that. I
added the if statement in case one of the places that do set it does
call this.

In other words, I added the if statement to make it more robust and
prevent a bug in the future ;-)

-- Steve


> 
> Thank you,
> 
> > ---
> >  kernel/trace/trace.c | 33 ++++++++++++++++++++++-----------
> >  1 file changed, 22 insertions(+), 11 deletions(-)
> > 
> > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > index 1c370ffbe062..8775930aa545 100644
> > --- a/kernel/trace/trace.c
> > +++ b/kernel/trace/trace.c
> > @@ -4815,6 +4815,25 @@ static const struct seq_operations tracer_seq_ops = {
> >  	.show		= s_show,
> >  };
> >  
> > +/*
> > + * Note, as iter itself can be allocated and freed in different
> > + * ways, this function is only used to free its content, and not
> > + * the iterator itself. The only requirement to all the allocations
> > + * is that it must zero all fields (kzalloc), as freeing works with
> > + * ethier allocated content or NULL.
> > + */
> > +static void free_trace_iter_content(struct trace_iterator *iter)
> > +{
> > +	/* The fmt is either NULL, allocated or points to static_fmt_buf */
> > +	if (iter->fmt != static_fmt_buf)
> > +		kfree(iter->fmt);
> > +
> > +	kfree(iter->temp);
> > +	kfree(iter->buffer_iter);
> > +	mutex_destroy(&iter->mutex);
> > +	free_cpumask_var(iter->started);
> > +}
> > +
> >  static struct trace_iterator *
> >  __tracing_open(struct inode *inode, struct file *file, bool snapshot)
> >  {
> > @@ -4922,8 +4941,7 @@ __tracing_open(struct inode *inode, struct file *file, bool snapshot)
> >  
> >   fail:
> >  	mutex_unlock(&trace_types_lock);
> > -	kfree(iter->temp);
> > -	kfree(iter->buffer_iter);
> > +	free_trace_iter_content(iter);
> >  release:
> >  	seq_release_private(inode, file);
> >  	return ERR_PTR(-ENOMEM);
> > @@ -5002,11 +5020,7 @@ static int tracing_release(struct inode *inode, struct file *file)
> >  
> >  	mutex_unlock(&trace_types_lock);
> >  
> > -	mutex_destroy(&iter->mutex);
> > -	free_cpumask_var(iter->started);
> > -	kfree(iter->fmt);
> > -	kfree(iter->temp);
> > -	kfree(iter->buffer_iter);
> > +	free_trace_iter_content(iter);
> >  	seq_release_private(inode, file);
> >  
> >  	return 0;
> > @@ -6763,10 +6777,7 @@ static int tracing_release_pipe(struct inode *inode, struct file *file)
> >  
> >  	mutex_unlock(&trace_types_lock);
> >  
> > -	free_cpumask_var(iter->started);
> > -	kfree(iter->fmt);
> > -	kfree(iter->temp);
> > -	mutex_destroy(&iter->mutex);
> > +	free_trace_iter_content(iter);
> >  	kfree(iter);
> >  
> >  	trace_array_put(tr);
> > -- 
> > 2.40.1  
> 
>