linux-kernel - Re: [PATCH 2/2] ptrace: do not use task

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Date:	Mon, 4 May 2009 21:36:24 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Roland McGrath <roland@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jeff Dike <jdike@...toit.com>, utrace-devel@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] ptrace: do not use task_lock() for attach

On 05/04, Roland McGrath wrote:
>
> This looks good to me overall.  It might be worth slicing it into two or
> more patches, just for bisect paranoia.  (e.g. PF_KTHREAD; task_lock in
> ptrace_attach; task_lock in ptrace_traceme.)

OK,

> I think it merits a comment that the PF_KTHREAD check does not need any
> interlock because daemonize() will detach ptrace via reparent_to_kthreadd()
> after it sets PF_KTHREAD.  (vs the old ->mm check under task_lock.)

Agreed, but actually the patch doesn't make the difference wrt daemonize().
currently ptrace_attach() can take task_lock() just before daemonize() calls
exit_mm().

> It is worth noting that this changes the security_ptrace_traceme() call so
> it's no longer under task_lock().  I can't see any way the LSM hooks care,
> but it is a change.

Yes, good point.

> You also didn't mention the s/|=/=/ changes.  Those are correct, we've
> already agreed, but the commit log should mention that this subtle change
> was intentional.

Yes! Forgot to mention, thanks.

Oleg.

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