linux-kernel - Re: linux-next: add utrace tree

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Message-ID: <20100126233242.GA25575@redhat.com>
Date:	Wed, 27 Jan 2010 00:32:42 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>, tromey@...hat.com,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Kyle Moffett <kyle@...fetthome.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Peter Zijlstra <peterz@...radead.org>,
	Fr??d??ric Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	"Frank Ch. Eigler" <fche@...hat.com>, linux-next@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>, utrace-devel@...hat.com,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: linux-next: add utrace tree

On 01/26, Andi Kleen wrote:
>
> > Simple example. Try to debug/strace strace ot gdb itself. Not trivial,
> > you can't attach to strace's tracees. Recently I spent 2 days trying to
> > understand why strace -f hangs. I was able to attach to strace, but
> > I wasn't able to see what its tracees do.
>
> But what would the semantics be inside the tracees even if you could?

In this particular case, all I need was something like "gdb -p" to
attach to the tracee, see the backtrace and detach.

> > And, it was not possible to even trace strace until it hangs, with
> > ptrace the tracee (strace) must stop to report the event and this
> > shadowed the race.
>
> "Shadowing the race" was the second surname of strace I thought anyways @)
> Basically if you care about races never use strace in the first place.

Yes. And utrace doesn't require the tracee to be stopped to report the
event ;) Yes, yes, utrace can't "fix" strace in this sense automatically,
but still.

Oleg.

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