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Message-ID: <7d40d7190511090949xc550b68k@mail.gmail.com>
Date: Wed, 9 Nov 2005 18:49:01 +0100
From: Aritz Bastida <aritzbastida@gmail.com>
To: Arnd Bergmann <arnd@arndb.de>
Subject: Re: Stopping Kernel Threads at module unload time
Cc: "linux-os (Dick Johnson)" <linux-os@analogic.com>,
       linux-kernel@vger.kernel.org
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2005/11/9, Arnd Bergmann <arnd@arndb.de>:
> On Middeweken 09 November 2005 17:56, Aritz Bastida wrote:
> > Now, if I call kthread_stop() in module unload time, does that code
> > run in user process context just like system calls do? That is
> > important, because if it cannot sleep, it would deadlock.
>
> Yes, it runs in the context of the delete_module system call.
> I think it's more likely that you're not returning from your
> thread loop.
>
> Please post a URL for your module source code so we can see
> what goes wrong there.
>
>         Arnd <><

Than you very much Arnd!
You solved my problem. hehe

I began to write a test module for showing you this and have just
realized about the problem. As I create as many threads as CPUs, I
have to delete them all when finishing.

I killed them like this:

        /* We don't need the distraction of CPUs appearing and vanishing. */
        lock_cpu_hotplug();
        for_each_online_cpu(cpu) {
                p = per_cpu(ksensord_info, cpu);
                kthread_stop(p);
        }
        unlock_cpu_hotplug();

I locked the cpu hotplug lock to protect the for_each_online_cpu()
code in case a cpu appears/vanishes, so I am actually calling
kthread_stop() in an atomic context, so it wakes up the process, but
dont let it run!

This is quite a subtle error, but of course it's my complete fault :P
May be a BUG_ON(in_atomic()) within kthread_stop() would let this kind of
errors be acknowledged more easily.

Thank you for your help
Regards

Aritz Bastida