linux-kernel - Re: [bisected] rcu_sched detected stalls - 4.15 or newer kernel with some Xeon skylake CPUs and extended APIC

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Date:   Thu, 17 May 2018 14:36:39 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Rick Warner <rick@...roway.com>
cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [bisected] rcu_sched detected stalls - 4.15 or newer kernel with
 some Xeon skylake CPUs and extended APIC

Rick,

On Wed, 16 May 2018, Rick Warner wrote:

> I've attached the dmesg output with the kernel parameter and supplied patch.

Thanks for providing the data. I think I know what's wrong here. Does the
patch below fix your problem?

While you test, I go looking for a big brown paperbag.

Thanks,

	tglx

8<----------------

--- a/arch/x86/kernel/apic/x2apic_cluster.c
+++ b/arch/x86/kernel/apic/x2apic_cluster.c
@@ -124,6 +124,7 @@ static void init_x2apic_ldr(void)
 			goto update;
 	}
 	cmsk = cluster_hotplug_mask;
+	cmsk->clusterid = cluster;
 	cluster_hotplug_mask = NULL;
 update:
 	this_cpu_write(cluster_masks, cmsk);