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SubjectRe: [PATCH] printk: robustify printk
On Fri, 08 Aug 2008 20:14:28 +0200
Peter Zijlstra <a.p.zijlstra@chello.nl> 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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