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

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Message-ID: <55C0F291.7060806@citrix.com>
Date:	Tue, 4 Aug 2015 18:12:49 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	"Jason A. Donenfeld" <Jason@...c4.com>,
	<linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
	<xen-devel@...ts.xen.org>
CC:	Paul McKenney <paulmck@...ux.vnet.ibm.com>
Subject: Re: [Xen-devel] printk from softirq on xen: hard lockup

On 04/08/15 17:41, Jason A. Donenfeld wrote:
> Hi folks,
> 
> Paul McKenney and I had an offline discussion about some rcu questions
> that eventually lead into me investigating a strange full lock-up I'm
> experiencing as a consequence of a printk in softirq inside of an
> rcu_read_lock, when using Xen PV. Relevant excerpts of the
                                ^^  PV guest?

> (gdb) target remote localhost:9999
> Remote debugging using localhost:9999
> __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?

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

David
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