Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751262AbaK0PHP (ORCPT ); Thu, 27 Nov 2014 10:07:15 -0500 Received: from www.linutronix.de ([62.245.132.108]:57280 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751050AbaK0PHN (ORCPT ); Thu, 27 Nov 2014 10:07:13 -0500 Date: Thu, 27 Nov 2014 16:07:02 +0100 (CET) From: Thomas Gleixner To: Heiko Carstens cc: David Hildenbrand , "Michael S. Tsirkin" , Christian Borntraeger , linuxppc-dev@lists.ozlabs.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, benh@kernel.crashing.org, paulus@samba.org, akpm@linux-foundation.org, schwidefsky@de.ibm.com, mingo@kernel.org Subject: Re: [RFC 0/2] Reenable might_sleep() checks for might_fault() when atomic In-Reply-To: <20141127120441.GB4390@osiris> Message-ID: 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> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 27 Nov 2014, Heiko Carstens wrote: > On Thu, Nov 27, 2014 at 09:03:01AM +0100, David Hildenbrand wrote: > > > Code like > > > spin_lock(&lock); > > > if (copy_to_user(...)) > > > rc = ... > > > spin_unlock(&lock); > > > really *should* generate warnings like it did before. > > > > > > And *only* code like > > > spin_lock(&lock); > > > > Is only code like this valid or also with the spin_lock() dropped? > > (e.g. the access in patch1 if I remember correctly) > > > > So should page_fault_disable() increment the pagefault counter and the preempt > > counter or only the first one? > > Given that a sequence like > > page_fault_disable(); > if (copy_to_user(...)) > rc = ... > page_fault_enable(); > > is correct code right now I think page_fault_disable() should increase both. > No need for surprising semantic changes. OTOH, there is no reason why we need to disable preemption over that page_fault_disabled() region. There are code pathes which really do not require to disable preemption for that. We have that seperated in preempt-rt for obvious reasons and IIRC Peter Zijlstra tried to distangle it in mainline some time ago. I forgot why that never got merged. We tie way too much stuff on the preemption count already, which is a mightmare because we have no clear distinction of protection scopes. Thanks, tglx -- 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/