Re: 174cc7187e6f ACPICA: Tables: Back port acpi_get_table_with_size() and early_acpi_os_unmap_memory() from Linux kernel

[Borislav Petkov]

On Mon, Jan 09, 2017 at 02:18:31PM -0800, Paul E. McKenney wrote:
> @@ -690,6 +690,8 @@ void synchronize_rcu_expedited(void)
>  {
>  	struct rcu_state *rsp = rcu_state_p;
>  
> +	if (!rcu_scheduler_active)
> +		return;
>  	_synchronize_rcu_expedited(rsp, sync_rcu_exp_handler);
>  }
>  EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);

That doesn't work and it is because of those damn what goes before what
boot sequence issues :-\

We have:

rest_init()
|-> rcu_scheduler_starting()  ---> that sets rcu_scheduler_active = 1;
|-> kernel_thread(kernel_init, NULL, CLONE_FS);
|-> kernel_init()
|-> kernel_init_freeable()
|-> native_smp_prepare_cpus(setup_max_cpus)
|-> default_setup_apic_routing
|-> enable_IR_x2apic
|-> irq_remapping_prepare
|-> amd_iommu_prepare
|-> iommu_go_to_state
|-> acpi_put_table(ivrs_base);
|-> acpi_tb_put_table(table_desc);
|-> acpi_tb_invalidate_table(table_desc);
|-> acpi_tb_release_table(...)
|-> acpi_os_unmap_memory
|-> acpi_os_unmap_iomem
|-> acpi_os_map_cleanup
|-> synchronize_rcu_expedited()

Now here we have rcu_scheduler_active already set so the test doesn't
hit and we hang.

So we must do it differently.

-- 
Regards/Gruss,
    Boris.

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