lkml.org 
[lkml]   [2008]   [Oct]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: do_boot_cpu can deadlock?
    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.



    \
     
     \ /
      Last update: 2008-10-24 11:35    [W:0.028 / U:1.224 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site