Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752196AbbEGLXp (ORCPT ); Thu, 7 May 2015 07:23:45 -0400 Received: from e06smtp14.uk.ibm.com ([195.75.94.110]:59122 "EHLO e06smtp14.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752140AbbEGLXn (ORCPT ); Thu, 7 May 2015 07:23:43 -0400 Date: Thu, 7 May 2015 13:23:35 +0200 From: David Hildenbrand To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, mingo@redhat.com, yang.shi@windriver.com, bigeasy@linutronix.de, benh@kernel.crashing.org, paulus@samba.org, akpm@linux-foundation.org, heiko.carstens@de.ibm.com, schwidefsky@de.ibm.com, borntraeger@de.ibm.com, mst@redhat.com, tglx@linutronix.de, David.Laight@ACULAB.COM, hughd@google.com, hocko@suse.cz, ralf@linux-mips.org, herbert@gondor.apana.org.au, linux@arm.linux.org.uk, airlied@linux.ie, daniel.vetter@intel.com, linux-mm@kvack.org, linux-arch@vger.kernel.org Subject: Re: [PATCH RFC 01/15] uaccess: count pagefault_disable() levels in pagefault_disabled Message-ID: <20150507132335.51016fe4@thinkpad-w530> In-Reply-To: <20150507111231.GF23123@twins.programming.kicks-ass.net> References: <1430934639-2131-1-git-send-email-dahi@linux.vnet.ibm.com> <1430934639-2131-2-git-send-email-dahi@linux.vnet.ibm.com> <20150507102254.GE23123@twins.programming.kicks-ass.net> <20150507125053.5d2e8f0a@thinkpad-w530> <20150507111231.GF23123@twins.programming.kicks-ass.net> Organization: IBM Deutschland GmbH X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.27; 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: 15050711-0017-0000-0000-000003F5D0DB Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1293 Lines: 35 > On Thu, May 07, 2015 at 12:50:53PM +0200, David Hildenbrand wrote: > > Just to make sure we have a common understanding (as written in my cover > > letter): > > > > Your suggestion won't work with !CONFIG_PREEMPT (!CONFIG_PREEMPT_COUNT). If > > there is no preempt counter, in_atomic() won't work. > > But there is, we _always_ have a preempt_count, and irq_enter() et al. > _always_ increment the relevant bits. > > The thread_info::preempt_count field it never under PREEMPT_COUNT > include/asm-generic/preempt.h provides stuff regardless of > PREEMPT_COUNT. > > See how __irq_enter() -> preempt_count_add(HARDIRQ_OFFSET) -> > __preempt_count_add() _always_ just works. > > Its only things like preempt_disable() / preempt_enable() that get > munged depending on PREEMPT_COUNT/PREEMPT. > Sorry for the confusion. Sure, there is always the count. My point is that preempt_disable() won't result in an in_atomic() == true with !PREEMPT_COUNT, so I don't see any point in adding in to the pagefault handlers. It is not reliable. 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/