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

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Date:	Mon, 22 Jul 2013 19:04:42 +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 07/22, Masami Hiramatsu wrote:
>
> (2013/07/19 22:33), Oleg Nesterov wrote:
> > My only point, imho this is more complex than necessary.
>
> I see, so I'd like to see the fix. However, I'm not sure
> we have enough time to fix that cleanly.

I promise, tomorrow I'll re-send the RFC patches, so if you don't
like them we can switch back to refcounting.

Sorry for delay. Today I was busy with other bugs I "found" in
subsystem_open/etc code, but when I tried to fix them I realized
that I have misread this code.

> Note that except
> for the timing bug, we still leave a kernel bug which can
> easily be reproduced as Jovi reported.

Could you please remind ?

> >> OK, let me confirm that, would you mean we still need 2/4 - 4/4?
> >
> > Yes, yes.
>
> And those are depends on 1/4...

Not at all or I missed something (quite possible). Just 2/4 should
not check ->flags, of course. 3/4 looks "obviously fine", 4/4 was
already merged.

Oleg.

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