From patchwork Thu May 16 11:16:10 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Michael S. Tsirkin" X-Patchwork-Id: 2576891 Return-Path: X-Original-To: patchwork-linux-arm@patchwork.kernel.org Delivered-To: patchwork-process-083081@patchwork2.kernel.org Received: from casper.infradead.org (casper.infradead.org [85.118.1.10]) by patchwork2.kernel.org (Postfix) with ESMTP id 172BADFB7B for ; Thu, 16 May 2013 11:19:02 +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 1UcwCx-0008Lx-IR; Thu, 16 May 2013 11:18:51 +0000 Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1UcwCh-0000x8-Qb; Thu, 16 May 2013 11:18:35 +0000 Received: from mx1.redhat.com ([209.132.183.28]) by merlin.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1UcwCf-0000vs-Nd for linux-arm-kernel@lists.infradead.org; Thu, 16 May 2013 11:18:34 +0000 Received: from int-mx10.intmail.prod.int.phx2.redhat.com (int-mx10.intmail.prod.int.phx2.redhat.com [10.5.11.23]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id r4GBG1Ko015859 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Thu, 16 May 2013 07:16:01 -0400 Received: from redhat.com (vpn-202-80.tlv.redhat.com [10.35.202.80]) by int-mx10.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with SMTP id r4GBFqrA014555; Thu, 16 May 2013 07:15:53 -0400 Date: Thu, 16 May 2013 14:16:10 +0300 From: "Michael S. Tsirkin" To: linux-kernel@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-Disposition: inline In-Reply-To: X-Mutt-Fcc: =sent X-Scanned-By: MIMEDefang 2.68 on 10.5.11.23 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20130516_071833_901297_937827F5 X-CRM114-Status: GOOD ( 20.87 ) X-Spam-Score: -7.5 (-------) X-Spam-Report: SpamAssassin version 3.3.2 on merlin.infradead.org summary: Content analysis details: (-7.5 points) pts rule name description ---- ---------------------- -------------------------------------------------- -5.0 RCVD_IN_DNSWL_HI RBL: Sender listed at http://www.dnswl.org/, high trust [209.132.183.28 listed in list.dnswl.org] -0.0 SPF_HELO_PASS SPF: HELO matches SPF record -0.0 SPF_PASS SPF: sender matches SPF record -0.6 RP_MATCHES_RCVD Envelope sender domain matches handover relay domain -1.9 BAYES_00 BODY: Bayes spam probability is 0 to 1% [score: 0.0000] Cc: linux-m32r-ja@ml.linux-m32r.org, kvm@vger.kernel.org, Peter Zijlstra , 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 , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, Michal Simek , linux-m32r@ml.linux-m32r.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 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);