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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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