linux-kernel - Re: [PATCH] kthread: saa7134-tvaudio.c

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Date:	Wed, 30 Aug 2006 06:39:49 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Andrew Morton <akpm@...l.org>, video4linux-list@...hat.com,
	kraxel@...esex.org, Containers@...ts.osdl.org,
	linux-kernel@...r.kernel.org,
	Mauro Carvalho Chehab <mchehab@...radead.org>
Subject: Re: [PATCH] kthread: saa7134-tvaudio.c

ebiederm@...ssion.com (Eric W. Biederman) writes:

> Andrew Morton <akpm@...l.org> writes:
>
>> So in general, yes, the driver should be converted to the kthread API -
>> this is a requirement for virtualisation, but I forget why, and that's the
>> "standard" way of doing it.
>
> With the kthread api new kernel threads are started as children of keventd
> in well defined circumstances.  If you don't do this kernel threads
> can wind up sharing weird parts of a parent process's resources and
> locking resources in the kernel long past the time when they are
> actually used by anything a user space process can kill.
>
> We have actually witnessed this problem with the kernels filesystem mount
> namespace.  Mostly daemonize in the kernel unshares everything that
> could be a problem but the problem is sufficiently subtle it makes
> more sense to the change kernel threads.  So these weird and subtle
> dependencies go away.
>
> So in essence the container work needs the new kthread api for the
> same reasons everyone else does it is just more pronounced in that
> case.

That plus the obvious bit.  For the pid namespace we have to declare
war on people storing a pid_t values.  Either converting them to
struct pid * or removing them entirely.  Doing the kernel_thread to
kthread conversion removes them entirely.

Eric
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