Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751219AbaK0Q3J (ORCPT ); Thu, 27 Nov 2014 11:29:09 -0500 Received: from mx0.aculab.com ([213.249.233.131]:44860 "HELO mx0.aculab.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751173AbaK0Q3G convert rfc822-to-8bit (ORCPT ); Thu, 27 Nov 2014 11:29:06 -0500 From: David Laight To: "'David Hildenbrand'" 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 Thread-Topic: [RFC 0/2] Reenable might_sleep() checks for might_fault() when atomic Thread-Index: AQHQClV0/jzAGGN4U0aVkHiOIDETdJx0mueggAAC44CAAAjz4A== Date: Thu, 27 Nov 2014 16:27:50 +0000 Message-ID: <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> In-Reply-To: <20141127164555.4bcebfe8@thinkpad-w530> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.202.99.200] Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 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. 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. 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/