Re: Stopping Kernel Threads at module unload time

[linux-os (Dick Johnson)]

On Wed, 9 Nov 2005, Aritz Bastida wrote:

> 2005/11/9, Arnd Bergmann <arnd@xxxxxxxx>:
>> 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


Ah, yes.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.13.4 on an i686 machine (5589.55 BogoMips).
Warning : 98.36% of all statistics are fiction.
.

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