linux-kernel - Re: [PATCH] kthread: Spontaneous exit support

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Message-ID: <20070423165810.GA188@tv-sign.ru>
Date:	Mon, 23 Apr 2007 20:58:10 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Christoph Hellwig <hch@...radead.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	containers@...ts.osdl.org, linux-kernel@...r.kernel.org,
	Marcel Holtmann <marcel@...tmann.org>, rusty@...tcorp.com.au
Subject: Re: [PATCH] kthread: Spontaneous exit support

On 04/23, Christoph Hellwig wrote:
>
> On Sun, Apr 22, 2007 at 09:12:55PM -0600, Eric W. Biederman wrote:
> > 
> > This patch implements the kthread helper functions kthread_start
> > and kthread_end which make it simple to support a kernel thread
> > that may decided to exit on it's own before we request it to.
> > It is still assumed that eventually we will get around to requesting
> > that the kernel thread stop.
> 
> I don't think having to parallel APIs is a good idea, people will
> get utterly confused which one to use.  Better always grab a reference
> in kthread_create and drop it in kthread_stop.  For normal thread
> no change in behaviour and only slightly more code in the slowpath.
> 
> Of course it will need an audit for half-assed kthread conversion
> first to avoid task_struct reference count leaks.

In that case it is better to grab a reference in kthread(). This also
close the race when a new thread is woken (freezer) and exits before
kthread_create() does get_task_struct().

> In addition to that kthrad_end implementation look wrong. When
> the kthread has exited prematurely no one will call complete
> on kthread_stop_info.done before it's been setup.

This is not true anymore, see another patch from Eric

	kthread-enhance-kthread_stop-to-abort-interruptible-sleeps.patch

Oleg.

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