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