Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753071AbbEGLIk (ORCPT ); Thu, 7 May 2015 07:08:40 -0400 Received: from mail-wi0-f175.google.com ([209.85.212.175]:34824 "EHLO mail-wi0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752883AbbEGLIe (ORCPT ); Thu, 7 May 2015 07:08:34 -0400 Date: Thu, 7 May 2015 13:08:28 +0200 From: Ingo Molnar To: Christian Borntraeger Cc: Andrew Morton , David Hildenbrand , linux-kernel@vger.kernel.org, mingo@redhat.com, peterz@infradead.org, yang.shi@windriver.com, bigeasy@linutronix.de, benh@kernel.crashing.org, paulus@samba.org, heiko.carstens@de.ibm.com, schwidefsky@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 00/15] decouple pagefault_disable() from preempt_disable() Message-ID: <20150507110828.GA15284@gmail.com> References: <1430934639-2131-1-git-send-email-dahi@linux.vnet.ibm.com> <20150506150158.0a927470007e8ea5f3278956@linux-foundation.org> <20150507094819.GC4734@gmail.com> <554B43AA.1050605@de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <554B43AA.1050605@de.ibm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1999 Lines: 63 * Christian Borntraeger wrote: > Am 07.05.2015 um 11:48 schrieb Ingo Molnar: > > > > * Andrew Morton wrote: > > > >> On Wed, 6 May 2015 19:50:24 +0200 David Hildenbrand wrote: > >> > >>> As Peter asked me to also do the decoupling in one shot, this is > >>> the new series. > >>> > >>> I recently discovered that might_fault() doesn't call might_sleep() > >>> anymore. Therefore bugs like: > >>> > >>> spin_lock(&lock); > >>> rc = copy_to_user(...); > >>> spin_unlock(&lock); > >>> > >>> would not be detected with CONFIG_DEBUG_ATOMIC_SLEEP. The code was > >>> changed to disable false positives for code like: > >>> > >>> pagefault_disable(); > >>> rc = copy_to_user(...); > >>> pagefault_enable(); > >>> > >>> Whereby the caller wants do deal with failures. > >> > >> hm, that was a significant screwup. I wonder how many bugs we > >> subsequently added. > > > > So I'm wondering what the motivation was to allow things like: > > > > pagefault_disable(); > > rc = copy_to_user(...); > > pagefault_enable(); > > > > and to declare it a false positive? > > > > AFAICS most uses are indeed atomic: > > > > pagefault_disable(); > > ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval); > > pagefault_enable(); > > > > so why not make it explicitly atomic again? > > Hmm, I am probably misreading that, but it sound as you suggest to go back > to Davids first proposal > https://lkml.org/lkml/2014/11/25/436 > which makes might_fault to also contain might_sleep. Correct? Yes, but I'm wondering what I'm missing: is there any deep reason for making pagefaults-disabled sections non-atomic? Thanks, Ingo -- 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/