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

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 13 Apr 2007 21:13:13 -0600 ebiederm@xmission.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 wake_up_process in kthread_stop has been replaced by signal_wake_up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