From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wg0-f52.google.com (mail-wg0-f52.google.com [74.125.82.52]) by kanga.kvack.org (Postfix) with ESMTP id 11E876B0032 for ; Thu, 7 May 2015 07:12:48 -0400 (EDT) Received: by wgyo15 with SMTP id o15so39922878wgy.2 for ; Thu, 07 May 2015 04:12:47 -0700 (PDT) Received: from casper.infradead.org (casper.infradead.org. [2001:770:15f::2]) by mx.google.com with ESMTPS id qr7si3352727wic.24.2015.05.07.04.12.46 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 07 May 2015 04:12:46 -0700 (PDT) Date: Thu, 7 May 2015 13:12:31 +0200 From: Peter Zijlstra Subject: Re: [PATCH RFC 01/15] uaccess: count pagefault_disable() levels in pagefault_disabled Message-ID: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150507125053.5d2e8f0a@thinkpad-w530> Sender: owner-linux-mm@kvack.org List-ID: To: David Hildenbrand 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 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. -- 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