Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751580AbaK0QuA (ORCPT ); Thu, 27 Nov 2014 11:50:00 -0500 Received: from e06smtp11.uk.ibm.com ([195.75.94.107]:54699 "EHLO e06smtp11.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751557AbaK0Qt5 (ORCPT ); Thu, 27 Nov 2014 11:49:57 -0500 Date: Thu, 27 Nov 2014 17:49:25 +0100 From: David Hildenbrand To: David Laight Cc: Thomas Gleixner , "linux-arch@vger.kernel.org" , "Michael S. Tsirkin" , "Heiko Carstens" , "linux-kernel@vger.kernel.org" , Christian Borntraeger , "paulus@samba.org" , "schwidefsky@de.ibm.com" , "akpm@linux-foundation.org" , "linuxppc-dev@lists.ozlabs.org" , "mingo@kernel.org" Subject: Re: [RFC 0/2] Reenable might_sleep() checks for might_fault() when atomic Message-ID: <20141127174925.53e9d7a6@thinkpad-w530> In-Reply-To: <063D6719AE5E284EB5DD2968C1650D6D1C9FDDD6@AcuExch.aculab.com> References: <20141126151729.GB9612@redhat.com> <20141126152334.GA9648@redhat.com> <20141126163207.63810fcb@thinkpad-w530> <20141126154717.GB10568@redhat.com> <5475FAB1.1000802@de.ibm.com> <20141126163216.GB10850@redhat.com> <547604FC.4030300@de.ibm.com> <20141126170447.GC11202@redhat.com> <20141127070919.GA4390@osiris> <20141127090301.3ddc3077@thinkpad-w530> <20141127120441.GB4390@osiris> <20141127161905.7c6220ee@thinkpad-w530> <063D6719AE5E284EB5DD2968C1650D6D1C9FDD6A@AcuExch.aculab.com> <20141127164555.4bcebfe8@thinkpad-w530> <063D6719AE5E284EB5DD2968C1650D6D1C9FDDD6@AcuExch.aculab.com> Organization: IBM Deutschland GmbH X-Mailer: Claws Mail 3.10.1 (GTK+ 2.24.24; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14112716-0005-0000-0000-00000240DBC3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > From: David Hildenbrand [mailto:dahi@linux.vnet.ibm.com] > > > From: David Hildenbrand > > > ... > > > > Although it might not be optimal, but keeping a separate counter for > > > > pagefault_disable() as part of the preemption counter seems to be the only > > > > doable thing right now. I am not sure if a completely separated counter is even > > > > possible, increasing the size of thread_info. > > > > > > What about adding (say) 0x10000 for the more restrictive test? > > > > > > David > > > > > > > You mean as part of the preempt counter? > > > > The current layout (on my branch) is > > > > * PREEMPT_MASK: 0x000000ff > > * SOFTIRQ_MASK: 0x0000ff00 > > * HARDIRQ_MASK: 0x000f0000 > > * NMI_MASK: 0x00100000 > > * PREEMPT_ACTIVE: 0x00200000 > > > > I would have added > > * PAGEFAULT_MASK: 0x03C00000 > > I'm not sure where you'd need to add the bits. > > I think the above works because disabling 'HARDIRQ' implicitly > disables 'SOFTIRQ' and 'PREEMPT' (etc), so if 256+ threads > disable PREEMPT everything still works. AFAIK 256+ levels of preempt will break the system :) Therefore with CONFIG_DEBUG_PREEMPT we verify that we don't have any over/underflows. But such bugs can only be found with CONFIG_DEBUG_PREEMPT enabled. > > So if disabling pagefaults implies that pre-emption is disabled > (but SOFTIRQ is still allowed) then you need to insert your bit(s) > between 0xff00 and 0x00ff. > OTOH if disabling pre-emption implies that pagefaults are disabled > then you'd need to use the lsb and change all the above values. > > Which makes me think that 'PREEMPT_ACTIVE' isn't right at all. > Two threads disabling NMIs (or 32 disabling HARDIRQ) won't DTRT. With threads you mean levels? This is a per thread information. > > OTOH I'm only guessing at how this is used. > > David > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/