Re: do_boot_cpu can deadlock?

From: Cyrill Gorcunov
Date: Thu Oct 23 2008 - 14:49:25 EST

[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 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());
else {

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)?

- Cyrill -
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