linux-kernel - Re: [patch] inherited events not signalling parent on overflow

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Message-ID: <20150731092642.GT25159@twins.programming.kicks-ass.net>
Date:	Fri, 31 Jul 2015 11:26:42 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vince Weaver <vincent.weaver@...ne.edu>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	eranian@...gle.com, Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: [patch] inherited events not signalling parent on overflow

On Fri, Jul 31, 2015 at 12:42:06AM -0400, Vince Weaver wrote:
> On Thu, 11 Jun 2015, Peter Zijlstra wrote:
> 
> > Right, I had a peek earlier at how fasync worked but came away confused.
> > 
> > Today I seem to have had better luck. Installing fasync allocates memory
> > and sets filp->f_flags |= FASYNC, which upon the demise of the file
> > descriptor ensures the allocation is freed.
> > 
> > Now for perf, we can have the events stick around for a while after the
> > original FD is dead because of references from child events. With the
> > above patch these events would still have a pointer into this free'd
> > fasync. This is bad.
> > 
> > A further problem with the patch is that if the parent changes its
> > fasync state the children might lag and again have pointers into dead
> > space.
> > 
> > All is not lost though; does something like the below work?
> 
> I had meant to reply to this earlier but maybe I forgot.
> 
> I've been running with this patch for a month now and haven't had 
> problems, and it fixes the issue of inherited signals.  So it no one else 
> has issues with the patch it would be nice if it could be pushed upstream.

Great, thanks for testing. I'll go queue it.
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