From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [PATCH RFC 00/15] decouple pagefault_disable() from preempt_disable() Date: Thu, 7 May 2015 11:48:19 +0200 Message-ID: <20150507094819.GC4734@gmail.com> References: <1430934639-2131-1-git-send-email-dahi@linux.vnet.ibm.com> <20150506150158.0a927470007e8ea5f3278956@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20150506150158.0a927470007e8ea5f3278956@linux-foundation.org> Sender: owner-linux-mm@kvack.org To: Andrew Morton Cc: 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, 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 List-Id: linux-arch.vger.kernel.org * 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? 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 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f179.google.com ([209.85.212.179]:38427 "EHLO mail-wi0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752548AbbEGJsZ (ORCPT ); Thu, 7 May 2015 05:48:25 -0400 Date: Thu, 7 May 2015 11:48:19 +0200 From: Ingo Molnar Subject: Re: [PATCH RFC 00/15] decouple pagefault_disable() from preempt_disable() Message-ID: <20150507094819.GC4734@gmail.com> References: <1430934639-2131-1-git-send-email-dahi@linux.vnet.ibm.com> <20150506150158.0a927470007e8ea5f3278956@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150506150158.0a927470007e8ea5f3278956@linux-foundation.org> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Andrew Morton Cc: 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, 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 Message-ID: <20150507094819.aLMnPO41EDTWS4F9NkFtE4vqEkwxNqV3xLtF87pZA7g@z> * 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? Thanks, Ingo