linux-kernel - Re: [PATCH] kthread: Enhance kthread_stop to abort interruptible sleeps

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Date:	Tue, 24 Apr 2007 03:09:24 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	ebiederm@...ssion.com (Eric W. Biederman)
Cc:	Oleg Nesterov <oleg@...sign.ru>,
	Davide Libenzi <davidel@...ilserver.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Roland McGrath <roland@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org, <linux-arch@...r.kernel.org>
Subject: Re: [PATCH] kthread: Enhance kthread_stop to abort interruptible
 sleeps

On Fri, 13 Apr 2007 21:13:13 -0600 ebiederm@...ssion.com (Eric W. Biederman) wrote:

> This patch reworks kthread_stop so it is more flexible and it causes
> the target kthread to abort interruptible sleeps.  Allowing a larger
> class of kernel threads to use to the kthread API.
> 
> The changes start by defining TIF_KTHREAD_STOP on all architectures.
> TIF_KTHREAD_STOP is a per process flag that I can set from another
> process to indicate that a kernel thread should stop.
> 
> wake_up_process in kthread_stop has been replaced by signal_wake_up
> ensuring that the kernel thread if sleeping is woken up in a timely
> manner and with TIF_SIGNAL_PENDING set, which causes us to break out
> of interruptible sleeps.
> 
> recalc_signal_pending was modified to keep TIF_SIGNAL_PENDING set for
> as long as TIF_KTHREAD_STOP is set.
> 
> Arbitrary paths to do_exit are now allowed.  I have placed a
> completion on the thread stack and pointed vfork_done at it, when the
> mm_release is called from do_exit the completion will be called.
> Since the completion is stored on the stack it is important that
> kthread() now calls do_exit ensuring the stack frame that holds the
> completion is never released, and so that our exit_code is certain to
> make it unchanged all the way to do_exit.
> 
> To allow kthread_stop to read the process exit code when exit_mm wakes
> it up  I have moved the setting of exit_code to the beginning of
> do_exit. 

This patch causes this oops: http://userweb.kernel.org/~akpm/s5000508.jpg
with this config: http://userweb.kernel.org/~akpm/config-x.txt
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