linux-kernel - Re: [PATCH] tracing: fix referencing after memory freeing and refactors code

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Date:	Sat, 19 Oct 2013 11:41:10 -0300
From:	Geyslan Gregório Bem <geyslan@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	kernel-br <kernel-br@...glegroups.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	open list <linux-kernel@...r.kernel.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Subject: Re: [PATCH] tracing: fix referencing after memory freeing and
 refactors code

2013/10/19 Oleg Nesterov <oleg@...hat.com>:
> On 10/19, Geyslan Gregório Bem wrote:
>>
>> 2013/10/19 Oleg Nesterov <oleg@...hat.com>:
>> > On 10/17, Steven Rostedt wrote:
>> >>
>> >> I'm thinking of just nuking the tracing_open_generic() here. The only
>> >> thing it does here is the tracing_disabled check. The assignment of
>> >> inode->i_private to filp->private_data is pointless
>> >
>> > The same for ftrace_enable_fops() and ftrace_event_filter_fops() at
>> > least. The users of event_file_data() do not use ->private_data.
>> >
>>
>> Aren't "ftrace_enable_fops" and "ftrace_event_filter_fops" structures?
>
> I meant, their ->open() methods.

I see.
>
>> About event_file_data() I think that the callers uses the
>> private_data. So, we have to analyze better.
>
> No, event_file_data() uses ->i_private, filp->private_data is not used.
> And it can't be used, it can point to the already destroyed/freed data.

Ok. I got it.
>
> but, as for seq_open() users,
>
>> static int trace_format_open(struct inode *inode, struct file *file)
>> {
>>     struct seq_file *m;
>>     int ret;
>>
>>     ret = seq_open(file, &trace_format_seq_ops);
>>     if (ret < 0)
>>         return ret;
>>
>>     m = file->private_data;
>>     m->private = file;
>>
>>     return 0;
>> }
>>
>> I really got confused here. The 'm' assignments are, to me, pointless.
>
> I confused too... Why do you think it is pointless?
>
> Just in case, not that after seq_open() ->private_data points to seq_file
> but it is still "void *". And in this case ->private_data has nothing to
> do with ->private_data  set by tracing_open_generic().
>

My bad. I realized it now.
> Oleg.
>

Let's wait Steve's reply about further use of tracing_is_disabled().

Regards.
--Geyslan
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