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SubjectRe: [PATCH] printk: robustify printk
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On Fri, 2008-08-08 at 12:14 -0700, Andrew Morton wrote:
> 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.

Drad, missed that bit, I did look at the calling end, but forgot the
call_rcu() end :-/

The initial printk_tick() based implementation didn't suffer this
problem, should we revert to that scheme?



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