Messages in this thread | | | Date | Fri, 24 Oct 2008 11:33:42 +0200 | From | Oleg Nesterov <> | Subject | Re: do_boot_cpu can deadlock? |
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On 10/23, Cyrill Gorcunov wrote: > > [Gautham R Shenoy - Thu, Oct 23, 2008 at 11:51:19PM +0530] > | On Thu, Oct 23, 2008 at 07:02:12PM +0200, Oleg Nesterov wrote: > | > Hmm. arch/x86/kernel/smpboot.c:do_boot_cpu() can deadlock ? > | > > | > It is called from _cpu_up() under cpu_hotplug_begin(), and it > | > waits for c_idle.work. Again, if we have the pending work which > | > needs get_online_cpus() we seem to have problems. > | > | Good point. Though this code gets triggered mostly during boot time when > | the CPUs are being brought online for the first time. If we have some > | work-item pending at that time, which needs get_online_cpus(), we could > | possibly see this deadlock. > | > | > > | > Oleg. > | > | -- > | Thanks and Regards > | gautham > | > > May I ask? If I understand right we do use this part of do_boot_cpu > > if (!keventd_up() || current_is_keventd()) > c_idle.work.func(&c_idle.work); > else { > schedule_work(&c_idle.work); > wait_for_completion(&c_idle.done); > } > > if only we've been called the first time after power on. And all > subsequent call of this do_boot_cpu would lead to > > if (c_idle.idle) { > c_idle.idle->thread.sp = (unsigned long) (((struct pt_regs *) > (THREAD_SIZE + task_stack_page(c_idle.idle))) - 1); > init_idle(c_idle.idle, cpu); > goto do_rest; > } > > ie go to do_rest and no wait_for_completion/schedule_work at all. > Did I miss something? *Sorry* in advance if the question is quite > not related. This work-pending situation is in 'possible' scenario > only (ie we don't have such a callers for now... yet)?
There are no problems during boot time, afaics.
kernel_init() calls smp_init() before do_basic_setup()->init_workqueues(). This means that do_boot_cpu() won't use workqueues due to !keventd_up().
But let's suppose we boot with maxcpus=1, and then bring up another CPU. Or we really add the new physical CPU (I don't really know if this is possible on x86).
Oleg.
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