linux-kernel - Re: [PATCH -mm 0/3] ptrace: detach wakeup fixes

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Date:	Mon, 9 Feb 2009 02:43:55 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Roland McGrath <roland@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jerome Marchand <jmarchan@...hat.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm 0/3] ptrace: detach wakeup fixes

On 02/08, Roland McGrath wrote:
>
> > Q: when the tracer exits we bypass ptrace_disable() and
> > clear_tsk_thread_flag(TIF_SYSCALL_TRACE), is this correct?
>
> It's always been that way.  It's obviously wrong in an abstract sense.  But
> for me, ptrace today is purely about compatibility with how it's behaved in
> the past, however stupid that was--whenever it's been fully consistent and
> predictable, userland is already saddled with coping with the stupidity.
>
> > Perhaps we should move this code into __ptrace_unlink?
>
> Locking nightmare.  ptrace_disable can do stuff that may require the thread
> to be stopped like other ptrace operations require (fiddle registers),
> might include access_process_vm, etc.  Trust me, we don't want to go there
> now.

OK, thanks.

> (In case you were looking for reasons why I'll be soon advocating
> reorganization to get ptrace entirely out of the tasklist_lock arena, this
> is a fine example of the true horror that the current data structure set-up
> gives us.)

Heh. No, I don't need yet another reason to remove tasklist from ptrace ;)
This would be obviously great.

(btw, I do remember I promised the cleanup, will send a bit later).

Oleg.

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