Messages in this thread | | | From | (Eric W. Biederman) | Subject | Re: [PATCH] kthread: Spontaneous exit support | Date | Mon, 23 Apr 2007 11:45:51 -0600 |
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Oleg Nesterov <oleg@tv-sign.ru> writes:
> 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
Ok. Thinking about it I agree with Christoph that parallel API's can be a problem.
However we do still need to support kernel threads where kthread_stop will never be called. There appear to be a few legitimate cases where someone wants to fire off a thread and have it do some work but don't care at all for stopping it before it is done.
So I propose we add a kthread_orphan as a basic primitive to decrement the count on the task_struct if we want a kthread to simply exit after it has done some work.
And as a helper function we can have a kthread_run_orphan.
I think having a kthread_orphan will document what we are doing better and make it easy to find kernel threads that don't use kthread_stop.
The pain is that this requires an audit of all kernel kthread creators so that we call kthread_orphan on the right ones, or else we will have a task_struct leak. At least that isn't a fatal condition.
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