Re: Dumb question: BKL on reboot ?

Andrew Morton
2003-08-20T18:27:28Z

Hannes Reinecke <Hannes.Reinecke@suse.de> wrote:
>
> Hiya,
>
> I've got a dumb question: Why is the BKL held on entering sys_reboot()
> in kernel/sys.c:405 ?

Probably for no good reason.

> It is getting especially interesting on SMP, when one cpu is entering
> sys_reboot, acquires the BKL and then waits (via machine_restart) for
> all other cpus to shut down. If any of the other cpus is executing a
> task which also needs the BKL, we have a nice deadlock.
> We've seen this here on 2-way s390, where the other cpu tried to execute
> kupdated() (what did it try that for? Anyway...), which of course
> resulted in a deadlock.

I guess that dropping the BKL around the machine_restart() call would be an
appropriate 2.4 fix.

Where exactly does the rebooting CPU get stuck in machine_restart()? If
someone has done lock_kernel() with local interrupts disabled then yes,
it'll deadlock. But that's unlikely? Confused.