linux-kernel - Re: [PATCH 2/4] pids: init_struct_pid.tasks should never see the swapper process

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Date:	Wed, 12 May 2010 18:03:59 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Cedric Le Goater <clg@...t.ibm.com>,
	Dave Hansen <haveblue@...ibm.com>,
	Eric Biederman <ebiederm@...ssion.com>,
	Herbert Poetzl <herbert@...hfloor.at>,
	Ingo Molnar <mingo@...e.hu>,
	Mathias Krause <Mathias.Krause@...unet.com>,
	Roland McGrath <roland@...hat.com>,
	Sukadev Bhattiprolu <sukadev@...ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] pids: init_struct_pid.tasks should never see the
	swapper process

On 05/11, Serge E. Hallyn wrote:
>
> Quoting Oleg Nesterov (oleg@...hat.com):
> > Change INIT_STRUCT_PID/INIT_PID_LINK to create the empty/unhashed
> > hlist_head/hlist_node. Like any other idle thread swapper can never exit,
> > so detach_pid()->__hlist_del() is not possible, but we could change
> > INIT_PID_LINK() to set pprev = &next if needed.
> >
> > All we need is the valid swapper->pids[].pid == &init_struct_pid.
> >
> > Reported-by: Mathias Krause <mathias.krause@...unet.com>
>
> Crimey, trying to find some way this could get dereferenced,

Yes, I was worried too. But afaics we should never use this hlist_node.
Except, of course, it is linked into pid->task.

> finding
> myself impressed with the likes of set_ftrace_swapper().
>
> Anyway, not finding anything, so
>
> > Signed-off-by: Oleg Nesterov <oleg@...hat.com>
>
> Acked-by: Serge E. Hallyn <serue@...ibm.com>

Thanks for review!

Oleg.

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