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SubjectRe: [PATCH] kthread_worker: Initialize dynamically allocated spinlock properly for lockdep
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On Sun, Dec 19, 2010 at 8:49 PM, Andy Walls <awalls@md.metrocast.net> wrote:
> init_kthread_worker(), via KTHREAD_WORKER_INIT(), used an
> initializer for static spin_lock objects, SPIN_LOCK_UNLOCKED, on
> a dynamically allocated kthread_worker object's internal spinlock_t.
> This causes lockdep to gripe:
>
>        INFO: trying to register non-static key.
>        the code is fine but needs lockdep annotation.
>        turning off the locking correctness validator.
>
> To keep lockdep happy, use spin_lock_init() for dynamically
> allocated kthread_worker objects' internal spinlock_t.
>
> Reported-by: Nicolas <nicolas.mailhot@laposte.net>
> Signed-off-by: Andy Walls <awalls@md.metrocast.net>
>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Jarod Wilson <jarod@redhat.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Mauro Carvalho Chehab <mchehab@redhat.com>
> Cc: Hans Verkuil <hverkuil@xs4all.nl>
>
> diff --git a/include/linux/kthread.h b/include/linux/kthread.h
> index 685ea65..e65d0b1 100644
> --- a/include/linux/kthread.h
> +++ b/include/linux/kthread.h
> @@ -83,7 +83,13 @@ struct kthread_work {
>
>  static inline void init_kthread_worker(struct kthread_worker *worker)
>  {
> -       *worker = (struct kthread_worker)KTHREAD_WORKER_INIT(*worker);
> +       /*
> +        * Lockdep complains if a dynamically allocated worker's spinlock_t
> +        * is initialzed using SPIN_LOCK_UNLOCKED.
> +        */
> +       spin_lock_init(&worker->lock);

This will make different kthead_worker->lock initialized with one same
key. You know spin_lock_init() will be like below:
# define raw_spin_lock_init(lock) \
do { \
static struct lock_class_key __key; \
\
__raw_spin_lock_init((lock), #lock, &__key); \
} while (0)
So we should put the real initializer to kernel/kthread.c
and make init_kthread_worker() to be a MACRO.

BTW, init_kthread_work() should also be changed like above
because member done is a wait_queue_head.

Thanks,
Yong

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