linux-kernel - Re: [PATCH] vt: Rework the console spawning variables.

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Date:	Mon, 11 Sep 2006 06:59:40 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org,
	Linux Containers <containers@...ts.osdl.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] vt: Rework the console spawning variables.

On 09/10, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg@...sign.ru> writes:
> 
> > On 09/10, Eric W. Biederman wrote:
> >>
> >> Updating this old code is painful.
> >
> > No, no, we shouldn't change the old code, it is fine.
> >
> So what happens when:
> cpu0:                         cpu1:
> kill_pid(vt_pid,....)         fn_SAK()->vc_reset()->put_pid(xchg(&vt_pid, NULL))
> 
> Can't kill_pid dereference vt_pid after put_pid is called?

Ah, I didn't consider that patch as 'old code', sorry :)

I don't understand drivers/char/vt*, but surely put_pid(xchg()) can't work.
Again, unless we have a lock to serialize access to ->vt_pid, but in that
case we don't need xchg().

Oleg.

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