From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e06smtp14.uk.ibm.com (e06smtp14.uk.ibm.com [195.75.94.110]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 1253F1A09C8 for ; Thu, 27 Nov 2014 23:04:52 +1100 (AEDT) Received: from /spool/local by e06smtp14.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 27 Nov 2014 12:04:47 -0000 Received: from b06cxnps4075.portsmouth.uk.ibm.com (d06relay12.portsmouth.uk.ibm.com [9.149.109.197]) by d06dlp03.portsmouth.uk.ibm.com (Postfix) with ESMTP id 93E021B0804B for ; Thu, 27 Nov 2014 12:05:00 +0000 (GMT) Received: from d06av04.portsmouth.uk.ibm.com (d06av04.portsmouth.uk.ibm.com [9.149.37.216]) by b06cxnps4075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id sARC4jUC16187422 for ; Thu, 27 Nov 2014 12:04:45 GMT Received: from d06av04.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av04.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id sARC4feF003367 for ; Thu, 27 Nov 2014 05:04:44 -0700 Date: Thu, 27 Nov 2014 13:04:41 +0100 From: Heiko Carstens To: David Hildenbrand Subject: Re: [RFC 0/2] Reenable might_sleep() checks for might_fault() when atomic Message-ID: <20141127120441.GB4390@osiris> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20141127090301.3ddc3077@thinkpad-w530> Cc: linux-arch@vger.kernel.org, "Michael S. Tsirkin" , 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 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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. > So we would have pagefault code rely on: > > in_disabled_pagefault() ( pagefault_disabled() ... whatever ) instead of > in_atomic(). No, let's be more defensive: the page fault handler should do nothing if in_atomic() just like now. But it could have a quick check and emit a one time warning if page faults aren't disabled in addition. That might help debugging but keeps the system more likely alive. might_fault() however should call might_sleep() if page faults aren't disabled, but that's what you proposed anyway I think.