On Sat, Jan 5, 2013 at 4:31 PM, Li Zhong <[email protected]> wrote: > On Sat, 2013-01-05 at 12:26 +0800, Hui Zhu wrote: >> The comments of these WARN_ON_ONCE said "Can deadlock when called with >> interrupts disabled". >> But I didn't find anything that will block this function. > > It seems that if two cpus try to IPI each other with wait equals true, > they will deadlock if interrupts are disabled, because neither of them > can take the interrupt. > > If wait equals false, it seems deadlock is still possible, for example, > if smp_call_function_single() is called from interrupt context, then one > cpu might > -->call smp_call_function_single() > -->csd_lock() > -->be interrupted before sending the ipi out > -->in interrupt context, call smp_call_function_single() again > -->csd_lock_wait() forever in csd_lock()
Thanks for your mail. It make me more clear about these functions. Best, Hui > > I'm not sure whether it is possible that irqs be enabled in interrupt > context? If so, maybe we also need check that if wait equals false? > > Thanks, Zhong > >> So I think maybe this WARN_ON_ONCE is not need now. So I post a patch for >> that. >> >> Signed-off-by: Hui Zhu <[email protected]> >> Signed-off-by: Zhu Yanhai <[email protected]> >> >> --- a/kernel/smp.c >> +++ b/kernel/smp.c >> @@ -303,25 +303,13 @@ int smp_call_function_single(int cpu, sm >> .flags = 0, >> }; >> unsigned long flags; >> - int this_cpu; >> int err = 0; >> >> /* >> * prevent preemption and reschedule on another processor, >> * as well as CPU removal >> */ >> - this_cpu = get_cpu(); >> - >> - /* >> - * Can deadlock when called with interrupts disabled. >> - * We allow cpu's that are not yet online though, as no one else can >> - * send smp call function interrupt to this cpu and as such deadlocks >> - * can't happen. >> - */ >> - WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled() >> - && !oops_in_progress); >> - >> - if (cpu == this_cpu) { >> + if (cpu == get_cpu()) { >> local_irq_save(flags); >> func(info); >> local_irq_restore(flags); >> @@ -409,17 +397,7 @@ void __smp_call_function_single(int cpu, >> unsigned int this_cpu; >> unsigned long flags; >> >> - this_cpu = get_cpu(); >> - /* >> - * Can deadlock when called with interrupts disabled. >> - * We allow cpu's that are not yet online though, as no one else can >> - * send smp call function interrupt to this cpu and as such deadlocks >> - * can't happen. >> - */ >> - WARN_ON_ONCE(cpu_online(smp_processor_id()) && wait && irqs_disabled() >> - && !oops_in_progress); >> - >> - if (cpu == this_cpu) { >> + if (cpu == get_cpu()) { >> local_irq_save(flags); >> data->func(data->info); >> local_irq_restore(flags); >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in >> the body of a message to [email protected] >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> Please read the FAQ at http://www.tux.org/lkml/ >> > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
