netdev - Re: [Xen-devel] printk from softirq on xen: hard lockup

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Date:	Wed, 5 Aug 2015 01:01:25 +0200
From:	"Jason A. Donenfeld" <Jason@...c4.com>
To:	David Vrabel <david.vrabel@...rix.com>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	xen-devel@...ts.xen.org, Paul McKenney <paulmck@...ux.vnet.ibm.com>
Subject: Re: [Xen-devel] printk from softirq on xen: hard lockup

Hey David,

Sorry for the premature response on my phone earlier. Real reply follows.
>> rcu_read_lock, when using Xen PV. Relevant excerpts of the
>                                 ^^  PV guest?

Yes. The lockup occurs on a PV guest. Nothing special at all about the
configuration. Vanilla upstream 4.1.3 kernel.

>> __xapic_wait_icr_idle () at ./arch/x86/include/asm/ipi.h:56
>> 56              while (native_apic_mem_read(APIC_ICR) & APIC_ICR_BUSY)
>                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^  => HVM guest
>
> Which is it?

That's odd. It's a PV guest, not an HVM nor PVH guest.

>
> A HVM guest's serial console may be particularly slow (since it's
> emulated by qemu).  Try using the PV console?

I am using the PV console. But actually the problem occurs too even if
/proc/sys/kernel/printk is set to all zeros (no klog on the console).

The plot thickens?
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