linux-kernel - Re: 174cc7187e6f ACPICA: Tables: Back port acpi_get_table_with_size() and early_acpi_os_unmap

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Date:   Tue, 10 Jan 2017 00:40:39 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     "Zheng, Lv" <lv.zheng@...el.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "Moore, Robert" <robert.moore@...el.com>,
        J?rg R?del <joro@...tes.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>
Subject: Re: 174cc7187e6f ACPICA: Tables: Back port
 acpi_get_table_with_size() and early_acpi_os_unmap_memory() from Linux
 kernel

On Mon, Jan 09, 2017 at 03:32:04PM -0800, Paul E. McKenney wrote:
> We could move rcu_scheduler_starting() later, as long as there
> is no chance of preemption or context switch before it is invoked.
> Would that help in this case, or are we already context switching before
> acpi_os_map_cleanup() is invoked?  (If we are already context switching,
> short-circuiting synchronize_rcu_expedited() would be a bug.)

Hmm, how about the below?

It would still happen before

        /*
         * The boot idle thread must execute schedule()
         * at least once to get things moving:
         */
        init_idle_bootup_task(current);
        schedule_preempt_disabled();

in rest_init() and right after native_smp_prepare_cpus() which is where
we're splatting.

Lemme run it.

Even if it works, we would have to stress-test this seriously...

---
diff --git a/init/main.c b/init/main.c
index b0c9d6facef9..9be221cc87c3 100644
--- a/init/main.c
+++ b/init/main.c
@@ -385,7 +385,6 @@ static noinline void __ref rest_init(void)
 {
 	int pid;
 
-	rcu_scheduler_starting();
 	/*
 	 * We need to spawn init first so that it obtains pid 1, however
 	 * the init task will end up wanting to create kthreads, which, if
@@ -1019,6 +1018,8 @@ static noinline void __init kernel_init_freeable(void)
 
 	smp_prepare_cpus(setup_max_cpus);
 
+	rcu_scheduler_starting();
+
 	workqueue_init();
 
 	do_pre_smp_initcalls();


-- 
Regards/Gruss,
    Boris.

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