From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e06smtp17.uk.ibm.com (e06smtp17.uk.ibm.com [195.75.94.113]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 95D3E1A0969 for ; Thu, 27 Nov 2014 19:03:13 +1100 (AEDT) Received: from /spool/local by e06smtp17.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 27 Nov 2014 08:03:09 -0000 Received: from b06cxnps4075.portsmouth.uk.ibm.com (d06relay12.portsmouth.uk.ibm.com [9.149.109.197]) by d06dlp01.portsmouth.uk.ibm.com (Postfix) with ESMTP id 4AE1117D8059 for ; Thu, 27 Nov 2014 08:03:23 +0000 (GMT) Received: from d06av03.portsmouth.uk.ibm.com (d06av03.portsmouth.uk.ibm.com [9.149.37.213]) by b06cxnps4075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id sAR837rf10551484 for ; Thu, 27 Nov 2014 08:03:07 GMT Received: from d06av03.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av03.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id sAR834Db006502 for ; Thu, 27 Nov 2014 01:03:06 -0700 Date: Thu, 27 Nov 2014 09:03:01 +0100 From: David Hildenbrand To: Heiko Carstens Subject: Re: [RFC 0/2] Reenable might_sleep() checks for might_fault() when atomic Message-ID: <20141127090301.3ddc3077@thinkpad-w530> In-Reply-To: <20141127070919.GA4390@osiris> References: <20141126070258.GA25523@redhat.com> <20141126110504.511b733a@thinkpad-w530> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII 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: , > 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? > page_fault_disable(); > if (copy_to_user(...)) > rc = ... > page_fault_enable(); > spin_unlock(&lock); > should not generate warnings, since the author hopefully knew what he did. > > We could achieve that by e.g. adding a couple of pagefault disabled bits > within current_thread_info()->preempt_count, which would allow > pagefault_disable() and pagefault_enable() to modify a different part of > preempt_count than it does now, so there is a way to tell if pagefaults have > been explicitly disabled or are just a side effect of preemption being > disabled. > This would allow might_fault() to restore its old sane behaviour for the > !page_fault_disabled() case. So we would have pagefault code rely on: in_disabled_pagefault() ( pagefault_disabled() ... whatever ) instead of in_atomic(). I agree with this approach, as this is basically what I suggested in one of my previous mails.