On Fri, Jul 05, 2013 at 03:50:57PM +0200, Thomas Gleixner wrote:
> On Sat, 16 Feb 2013, Chuansheng Liu wrote:
> > There is a real case for softirq DEADLOCK case:
> >
> > CPUA CPUB
> > spin_lock(&spinlock)
> > Any irq coming, call the irq handler
> > irq_exit()
> > spin_lock_irq(&spinlock)
> > <== Blocking here due to
> > CPUB hold it
> > __do_softirq()
> > run_timer_softirq()
> > timer_cb()
> > call smp_call_function_many()
> > send IPI interrupt to CPUA
> > wait_csd()
> >
> > Then both CPUA and CPUB will be deadlocked here.
>
Why can't we just use spin_lock_irq instead of spin_lock in CPUB to
prevent this to happen ?
And the according senario for kernel/smp.c is to use raw_spin_lock_irqsave
instead of raw_spin_lock in generic_smp_call_function_single_interrupt
to protect the follow one line codes:
raw_spin_lock(&q->lock);
list_replace_init(&q->list, &list);
raw_spin_unlock(&q->lock);
Thanks.
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