On Wed, 13 Mar 2013 18:47:05 +0100 Oleg Nesterov <o...@redhat.com> wrote:
> orderly_poweroff() can be used from any context but UMH_WAIT_EXEC
> is sleepable. Move the "force" logic into __orderly_poweroff() and
> change orderly_poweroff() to use the global poweroff_work which
> simply calls __orderly_poweroff().
>
> While at it, remove the unneeded "int argc" and change argv_split()
> to use GFP_KERNEL.
>
> We use the global "bool poweroff_force" to pass the argument, this
> can obviously affect the previous request if it is pending/running.
> So we only allow the "false => true" transition assuming that the
> pending "true" should succeed anyway. If schedule_work() fails after
> that we know that work->func() was not called yet, it must see the
> new value.
>
> This means that orderly_poweroff() becomes async even if we do not
> run the command and always succeeds, schedule_work() can only fail
> if the work is already pending. We can export __orderly_poweroff()
> and change the non-atomic callers which want the old semantics.
>
> ...
>
> @@ -2218,21 +2237,9 @@ static int __orderly_poweroff(void)
> */
> int orderly_poweroff(bool force)
> {
> - int ret = __orderly_poweroff();
> -
> - if (ret && force) {
> - printk(KERN_WARNING "Failed to start orderly shutdown: "
> - "forcing the issue\n");
> -
> - /*
> - * I guess this should try to kick off some daemon to sync and
> - * poweroff asap. Or not even bother syncing if we're doing an
> - * emergency shutdown?
> - */
> - emergency_sync();
> - kernel_power_off();
> - }
> -
> - return ret;
> + if (force) /* do not override the pending "true" */
> + poweroff_force = true;
> + schedule_work(&poweroff_work);
> + return 0;
> }
afaict the current version of orderly_poweroff() will never return -
either __orderly_poweroff() will block until the machine shuts down or
kernel_power_off() will do so.
However with this patch there is a path via which orderly_poweroff()
can return to its caller, I think? If so, the caller might be rather
surprised and we're exercising never-before-used code paths. In fact
if the surprised caller goes oops, the poweroff might not occur at all.
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