Re: [PATCH] kernel/kthread.c: need spin_lock_irq() for 'worker'before main looping, since it can "WARN_ON(worker->task)".

From: Tejun Heo
Date: Wed Jun 19 2013 - 04:41:39 EST


On Wed, Jun 19, 2013 at 12:03:38PM +0800, Chen Gang wrote:
>
> Since "WARN_ON(worker->task)", we can not assume that 'worker->task'
> will be NULL before set 'current' to it.
>
> So need let 'worker' lock protected too, just like it already lock
> protected all time in main looping.

That synchronization is the kthread_worker user's responsibility. The
locking around worker->task = NULL is to prevent the worker task being
destroyed while insert_kthread_work() is trying to wake it up. It has
nothing to do with the user trying to attach multiple tasks to the
same kthread_worker. Plus, putting locking around WARN_ON() is
pointless. It doesn't really fix anything. It just makes WARN_ON()
trigger *slightly* more reliably.

Thanks.

--
tejun
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