From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f170.google.com (mail-wi0-f170.google.com [209.85.212.170]) by kanga.kvack.org (Postfix) with ESMTP id 7BD606B0032 for ; Thu, 7 May 2015 07:25:08 -0400 (EDT) Received: by wizk4 with SMTP id k4so238403673wiz.1 for ; Thu, 07 May 2015 04:25:08 -0700 (PDT) Received: from mail-wi0-x22d.google.com (mail-wi0-x22d.google.com. [2a00:1450:400c:c05::22d]) by mx.google.com with ESMTPS id j18si2757333wjr.158.2015.05.07.04.25.05 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 07 May 2015 04:25:06 -0700 (PDT) Received: by wiun10 with SMTP id n10so55858472wiu.1 for ; Thu, 07 May 2015 04:25:05 -0700 (PDT) Date: Thu, 7 May 2015 13:25:01 +0200 From: Ingo Molnar Subject: Re: [PATCH RFC 01/15] uaccess: count pagefault_disable() levels in pagefault_disabled Message-ID: <20150507112501.GA15439@gmail.com> 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> <20150507132335.51016fe4@thinkpad-w530> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150507132335.51016fe4@thinkpad-w530> Sender: owner-linux-mm@kvack.org List-ID: To: David Hildenbrand Cc: Peter Zijlstra , 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 * David Hildenbrand wrote: > > 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. That's why we have the preempt_count_inc()/dec() methods that are always available. So where's the problem? Thanks, Ingo -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org