linux-kernel - Re: [RFC PATCH V2] tracing: Check f_dentry before accessing event_file/call in inode->i

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Date:	Wed, 17 Jul 2013 16:51:48 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	jovi.zhangwei@...wei.com, Jiri Olsa <jolsa@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH V2] tracing: Check f_dentry before accessing
	event_file/call in inode->i_private

On 07/17, Masami Hiramatsu wrote:
>
> (2013/07/16 3:16), Oleg Nesterov wrote:
> > On 07/09, Masami Hiramatsu wrote:
> >>
> >> To avoid this, when opening events/*/*/enable, we have to ensure
> >> the dentry of the file is not unlinked yet, under event_mutex
> >> is locked.
> >
> > Probably this can work, but I am starting to think that this ref
> > count becomes toooooo complex....
>
> Oleg, I agree that is a bit complex way to fix but it can fix.
>
> However, I think we should fix bugs first, because there are bugs.
> I don't like to leave a bug in the kernel as it is, while we re-
> start discussing new approach...

And I am trying to fix the same problems, just _I think_ there is
another and simpler approach.

> So, I'd like to suggest you getting these fixes into ftrace as
> first-aid treatment, and discuss your new series.

Well, perhaps you are right... But this TRACE_EVENT_FL_REF_MASK code
is new too, it is not that we only need a small fixlets to finish it.

So I think that it makes sense to discuss the alternatives before we
decide what exactly we should do.

Oleg.

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