Re: [PATCH] printk: robustify printk

[Andrew Morton]

On Fri, 08 Aug 2008 20:14:28 +0200
Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote:

>  void wake_up_klogd(void)
>  {
> -	if (!oops_in_progress && waitqueue_active(&log_wait))
> -		wake_up_interruptible(&log_wait);
> +	unsigned long flags;
> +	struct klogd_wakeup_state *kws;
> +
> +	if (!waitqueue_active(&log_wait))
> +		return;
> +
> +	local_irq_save(flags);
> +	kws = &__get_cpu_var(kws);
> +	if (!kws->pending) {
> +		kws->pending = 1;
> +		call_rcu(&kws->head, __wake_up_klogd);
> +	}
> +	local_irq_restore(flags);
>  }

Note that kernel/rcupreempt.c's flavour of call_rcu() takes
RCU_DATA_ME().lock, so there are still code sites from which a printk
can deadlock.  Only now, it is config-dependent.

>From a quick look it appears that large amounts of kernel/rcupreempt.c
are now a printk-free zone.

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