linux-kernel - Re: [PATCH 2/2] perf/tools: put new buildid locks to use

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Message-ID: <20150514173849.GB19338@gmail.com>
Date:	Thu, 14 May 2015 19:38:49 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Milos Vyletel <milos@...hat.com>
Cc:	Jiri Olsa <jolsa@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Jiri Olsa <jolsa@...nel.org>, He Kuang <hekuang@...wei.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	"open list:PERFORMANCE EVENT..." <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] perf/tools: put new buildid locks to use


* Milos Vyletel <milos@...hat.com> wrote:

> On Thu, May 14, 2015 at 01:38:21PM +0200, Jiri Olsa wrote:
> 
> > On Thu, May 14, 2015 at 12:40:59PM +0200, Ingo Molnar wrote:
> > > 
> > > * Milos Vyletel <milos@...hat.com> wrote:
> > > 
> > > > Use new read/write locks when accesing buildid directory on places where
> > > > we may race if multiple instances are run simultaneously.
> > > 
> > > Dunno, this will create locking interaction between multiple instances 
> > > of perf - hanging each other, etc.
> > > 
> > > And it seems unnecessary: the buildid hierarchy is already spread out. 
> > > What kind of races might there be?
> > 
> > there was just recently one fixed by commit:
> >   0635b0f71424 perf tools: Fix race in build_id_cache__add_s()
> > 
> > havent checked the final patch yet, but the idea is to
> > protect us from similar bugs
> 
> right. on top of race with EEXIST couple more are possible (EMLINK, 
> ENOSPC, EDQUOT, ENOMEM... the only way to prevent them all is to 
> lock this kind of operations and make sure we run one at a time.

No, that's not the only way to avoid the race - see my previous mail.

Thanks,

	Ingo
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