Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753246Ab3EPLT2 (ORCPT ); Thu, 16 May 2013 07:19:28 -0400 Received: from mx1.redhat.com ([209.132.183.28]:24102 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752993Ab3EPLTY (ORCPT ); Thu, 16 May 2013 07:19:24 -0400 Date: Thu, 16 May 2013 14:16:10 +0300 From: "Michael S. Tsirkin" To: linux-kernel@vger.kernel.org Cc: Catalin Marinas , Will Deacon , David Howells , Hirokazu Takata , Michal Simek , Koichi Yasutake , Benjamin Herrenschmidt , Paul Mackerras , Chris Metcalf , Thomas Gleixner , Ingo Molnar , Peter Zijlstra , "H. Peter Anvin" , x86@kernel.org, Arnd Bergmann , linux-arm-kernel@lists.infradead.org, linux-m32r@ml.linux-m32r.org, linux-m32r-ja@ml.linux-m32r.org, microblaze-uclinux@itee.uq.edu.au, linux-am33-list@redhat.com, linuxppc-dev@lists.ozlabs.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, kvm@vger.kernel.org Subject: [PATCH v2 10/10] kernel: might_fault does not imply might_sleep Message-ID: <1f85dc8e6a0149677563a2dfb4cef9a9c7eaa391.1368702323.git.mst@redhat.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Mutt-Fcc: =sent Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2445 Lines: 74 There are several ways to make sure might_fault calling function does not sleep. One is to use it on kernel or otherwise locked memory - apparently nfs/sunrpc does this. As noted by Ingo, this is handled by the migh_fault() implementation in mm/memory.c but not the one in linux/kernel.h so in the current code might_fault() schedules differently depending on CONFIG_PROVE_LOCKING, which is an undesired semantical side effect. Another is to call pagefault_disable: in this case the page fault handler will go to fixups processing and we get an error instead of sleeping, so the might_sleep annotation is a false positive. vhost driver wants to do this now in order to reuse socket ops under a spinlock (and fall back on slower thread handler on error). Address both issues by: - dropping the unconditional call to might_sleep from the fast might_fault code in linux/kernel.h - checking for pagefault_disable() in the CONFIG_PROVE_LOCKING implementation Signed-off-by: Michael S. Tsirkin --- include/linux/kernel.h | 1 - mm/memory.c | 14 +++++++++----- 2 files changed, 9 insertions(+), 6 deletions(-) diff --git a/include/linux/kernel.h b/include/linux/kernel.h index e96329c..322b065 100644 --- 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(); } #endif diff --git a/mm/memory.c b/mm/memory.c index 6dc1882..1b8327b 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4222,13 +4222,17 @@ void might_fault(void) 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. + * It would be nicer to annotate paths which are under preempt_disable + * but not under pagefault_disable, however that requires a new flag + * for differentiating between the two. */ - if (!in_atomic() && current->mm) + if (in_atomic()) + return; + + might_sleep(); + + if (current->mm) might_lock_read(¤t->mm->mmap_sem); } EXPORT_SYMBOL(might_fault); -- MST -- 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/