linux-kernel - Re: [PATCH 04/16] perf, mmap: Factor out perf_get

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Message-ID: <20140429153401.GK32718@rric.localhost>
Date:	Tue, 29 Apr 2014 17:34:01 +0200
From:	Robert Richter <rric@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jean Pihet <jean.pihet@...aro.org>, Borislav Petkov <bp@...en8.de>,
	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org,
	Al Viro <viro@...IV.linux.org.uk>
Subject: Re: [PATCH 04/16] perf, mmap: Factor out perf_get_fd()

On 25.04.14 16:52:05, Peter Zijlstra wrote:
> But no, I don't think that helps, its still true that the moment you get
> a fd another thread can immediately close(). That would drop the last
> ref and free it, meanwhile perf_event_open() is happily poking at it.
> 
> Now I think you could cure this by adding an extra ref before calling
> your perf_get_fd() and dropping that extra ref at the end, where we used
> to have fd_install().

Yes, right. I have a solution now which increments the event's ref
count before creating the file descriptor using try_get_event()/
put_event().

The patch also does not remove get_unused_fd_flags() and the err_fd
error handler.

Have an update already of a rebase version but still need to test it.

Would it be ok to split the patch set and send in a first step only
the first 4 patches that refactor the perf mmap code?

Thanks,

-Robert
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