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

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Message-Id: <20090504190935.A0FD4FC32F@magilla.sf.frob.com>
Date:	Mon,  4 May 2009 12:09:35 -0700 (PDT)
From:	Roland McGrath <roland@...hat.com>
To:	Oleg Nesterov <oleg@...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

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.)

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.)

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.

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.

Thanks,
Roland
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