From patchwork Tue May 21 11:57:34 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Peter Zijlstra X-Patchwork-Id: 2598761 Return-Path: X-Original-To: patchwork-linux-arm@patchwork.kernel.org Delivered-To: patchwork-process-083081@patchwork1.kernel.org Received: from casper.infradead.org (casper.infradead.org [85.118.1.10]) by patchwork1.kernel.org (Postfix) with ESMTP id 3DB803FE81 for ; Tue, 21 May 2013 18:34:08 +0000 (UTC) Received: from merlin.infradead.org ([2001:4978:20e::2]) by casper.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1Uemgs-0000nb-Fi; Tue, 21 May 2013 13:33:22 +0000 Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1UellG-00024K-K7; Tue, 21 May 2013 12:33:50 +0000 Received: from dhcp-089-099-019-018.chello.nl ([89.99.19.18] helo=twins) by merlin.infradead.org with esmtpsa (Exim 4.80.1 #2 (Red Hat Linux)) id 1Uell5-00022k-8z; Tue, 21 May 2013 12:33:39 +0000 Received: by twins (Postfix, from userid 1000) id A65C7827793D; Tue, 21 May 2013 13:57:34 +0200 (CEST) Date: Tue, 21 May 2013 13:57:34 +0200 From: Peter Zijlstra To: "Michael S. Tsirkin" Subject: Re: [PATCH v2 10/10] kernel: might_fault does not imply might_sleep Message-ID: <20130521115734.GA9554@twins.programming.kicks-ass.net> References: <1f85dc8e6a0149677563a2dfb4cef9a9c7eaa391.1368702323.git.mst@redhat.com> <20130516184041.GP19669@dyad.programming.kicks-ass.net> <20130519093526.GD19883@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20130519093526.GD19883@redhat.com> User-Agent: Mutt/1.5.21 (2012-12-30) Cc: linux-m32r-ja@ml.linux-m32r.org, kvm@vger.kernel.org, Catalin Marinas , Will Deacon , David Howells , linux-mm@kvack.org, Paul Mackerras , "H. Peter Anvin" , linux-arch@vger.kernel.org, linux-am33-list@redhat.com, Hirokazu Takata , x86@kernel.org, Ingo Molnar , Benjamin Herrenschmidt , Arnd Bergmann , microblaze-uclinux@itee.uq.edu.au, Chris Metcalf , rostedt@goodmis.org, Thomas Gleixner , linux-arm-kernel@lists.infradead.org, Michal Simek , linux-m32r@ml.linux-m32r.org, linux-kernel@vger.kernel.org, Koichi Yasutake , linuxppc-dev@lists.ozlabs.org X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org On Sun, May 19, 2013 at 12:35:26PM +0300, Michael S. Tsirkin wrote: > > > --- a/include/linux/kernel.h > > > +++ b/include/linux/kernel.h > > > @@ -198,7 +198,6 @@ void might_fault(void); > > > #else > > > static inline void might_fault(void) > > > { > > > - might_sleep(); > > > > This removes potential resched points for PREEMPT_VOLUNTARY -- was that > > intentional? > > No it's a bug. Thanks for pointing this out. > OK so I guess it should be might_sleep_if(!in_atomic()) > and this means might_fault would have to move from linux/kernel.h to > linux/uaccess.h, since in_atomic() is in linux/hardirq.h > > Makes sense? So the only difference between PROVE_LOCKING and not should be the might_lock_read() thing; so how about something like this? --- include/linux/kernel.h | 7 ++----- include/linux/uaccess.h | 26 ++++++++++++++++++++++++++ mm/memory.c | 14 ++------------ 3 files changed, 30 insertions(+), 17 deletions(-) diff --git a/include/linux/kernel.h b/include/linux/kernel.h index e96329c..70812f4 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -194,12 +194,9 @@ extern int _cond_resched(void); }) #ifdef CONFIG_PROVE_LOCKING -void might_fault(void); +void might_fault_lockdep(void); #else -static inline void might_fault(void) -{ - might_sleep(); -} +static inline void might_fault_lockdep(void) { } #endif extern struct atomic_notifier_head panic_notifier_list; diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h index 5ca0951..50a2cc9 100644 --- a/include/linux/uaccess.h +++ b/include/linux/uaccess.h @@ -38,6 +38,32 @@ static inline void pagefault_enable(void) preempt_check_resched(); } +static inline bool __can_fault(void) +{ + /* + * Some code (nfs/sunrpc) uses socket ops on kernel memory while + * holding the mmap_sem, this is safe because kernel memory doesn't + * get paged out, therefore we'll never actually fault, and the + * below annotations will generate false positives. + */ + if (segment_eq(get_fs(), KERNEL_DS)) + return false; + + if (in_atomic() /* || pagefault_disabled() */) + return false; + + return true; +} + +static inline void might_fault(void) +{ + if (!__can_fault()) + return; + + might_sleep(); + might_fault_lockdep(); +} + #ifndef ARCH_HAS_NOCACHE_UACCESS static inline unsigned long __copy_from_user_inatomic_nocache(void *to, diff --git a/mm/memory.c b/mm/memory.c index 6dc1882..266610c 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4211,19 +4211,9 @@ void print_vma_addr(char *prefix, unsigned long ip) } #ifdef CONFIG_PROVE_LOCKING -void might_fault(void) +void might_fault_lockdep(void) { /* - * Some code (nfs/sunrpc) uses socket ops on kernel memory while - * holding the mmap_sem, this is safe because kernel memory doesn't - * get paged out, therefore we'll never actually fault, and the - * below annotations will generate false positives. - */ - if (segment_eq(get_fs(), KERNEL_DS)) - return; - - might_sleep(); - /* * it would be nicer only to annotate paths which are not under * pagefault_disable, however that requires a larger audit and * providing helpers like get_user_atomic. @@ -4231,7 +4221,7 @@ void might_fault(void) if (!in_atomic() && current->mm) might_lock_read(¤t->mm->mmap_sem); } -EXPORT_SYMBOL(might_fault); +EXPORT_SYMBOL(might_fault_lockdep); #endif #if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)