linux-kernel - Re: [PATCH 10/11] tracing/perf: Fix lock events recursions in the fast path

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 05 Feb 2010 13:12:53 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>, paulmck@...ux.vnet.ibm.com,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Paul Mackerras <paulus@...ba.org>,
	Hitoshi Mitake <mitake@....info.waseda.ac.jp>,
	Li Zefan <lizf@...fujitsu.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [PATCH 10/11] tracing/perf: Fix lock events recursions in the
 fast path

On Fri, 2010-02-05 at 13:10 +0100, Peter Zijlstra wrote:
> On Fri, 2010-02-05 at 11:49 +0100, Ingo Molnar wrote:
> > 
> > > That said, I'm not at all happy about removing lockdep annotations to make 
> > > the tracer faster, that's really counter productive.
> > 
> > Are there no dynamic techniques that could be used here?
> > 
> > Lockdep obviously wants maximum instrumentation coverage - performance be 
> > damned.
> > 
> > Lock profiling/tracing/visualization wants the minimum subset of events it is 
> > interested in - everything else is unnecessary overhead.
> 
> Well, they could start by moving the tracepoint inside the lockdep
> recursion check.

IIRC the reason its now outside is that you'd loose tracepoint on
lockdep_off() usage, but having the tracer folks help on removing any
such usage is of course a good thing.

The usage thereof in nmi_enter() doesn't seem like a problem, since
you're not supposed to be using locks from nmi context anyway, more so,
I'd not be adverse to putting BUG_ON(in_nmi()) in every lockdep hook.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/