linux-kernel - Re: [PATCH 10/11] ptrace: move JOBCTL_TRAPPING wait to wait(2) and ptrace_check

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Message-ID: <20110512160709.GL1030@htj.dyndns.org>
Date:	Thu, 12 May 2011 18:07:09 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	jan.kratochvil@...hat.com, vda.linux@...glemail.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, indan@....nu
Subject: Re: [PATCH 10/11] ptrace: move JOBCTL_TRAPPING wait to wait(2) and
 ptrace_check_attach()

Hey,

On Thu, May 12, 2011 at 05:59:10PM +0200, Oleg Nesterov wrote:
> > I don't know.  Why is retrying hairy?  The whole waiting logic is
> > built for clean retries.  The suggested change just does it without
> > intervening sleeping and waking up.  I don't see anything particularly
> > hairy there.
> 
> As always, this is subjective. But I didn't mean -EAGAIN itself. In fact
> I was going to add this (simple) logic some time ago and kill the EXIT_DEAD
> state. Hmm, and I'd still like to do this...

Oh, I've been updating code and it's now using interruptible sleep +
-ERESTARTNOINTR return.  It's simpler and the freezer problem is gone
too.

> I meant the whole ptrace_wait_trapping() + lock dance + retry thing.
> But of course I do not pretend my feeling is right.

Yeah, it's more complex than I would have liked.  The problem is that
ptrace(2) isn't really equipped with facilities to handle async
events, so it's a bit painful to add async mechanism into the existing
mechanics, but most problems seem solvable.

> Also. _Perhaps_ we can rethink the SIGCONT trapping, and perhaps in
> this case do_wait() won't need any changes. May be.

But, if there's a better way, sure.

Thanks.

-- 
tejun
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