linux-kernel - Re: frequent lockups in 3.18rc4

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Message-ID: <20141119221819.GA24195@redhat.com>
Date:	Wed, 19 Nov 2014 17:18:19 -0500
From:	Dave Jones <davej@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Don Zickus <dzickus@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: frequent lockups in 3.18rc4

On Wed, Nov 19, 2014 at 11:38:09AM -0800, Linus Torvalds wrote:

 > > Is it possible that we've managed to return to userspace with
 > > interrupts off somehow?  A loop in userspace that somehow has
 > > interrupts off can cause all kinds of fun lockups.
 > 
 > That sounds unlikely, but if there is some stack corruption going on.
 > 
 > However, it wouldn't even explain things, because even if interrupts
 > had been disabled in user space, and even if that popf got executed,
 > this wouldn't be where they got enabled. That would be the :"sti" in
 > the system call entry path (hidden behind the ENABLE_INTERRUPTS
 > macro).
 > 
 > Of course, maybe Dave has paravirtualization enabled (what a crock
 > _that_ is), and there is something wrong with that whole code.

I've had HYPERVISOR_GUEST disabled for a while, which also disables
the paravirt code afaics.

	Dave

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