From patchwork Fri Jan 13 12:46:04 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Woodhouse X-Patchwork-Id: 13100737 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 06860C54EBE for ; Fri, 13 Jan 2023 13:01:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241433AbjAMNBH (ORCPT ); Fri, 13 Jan 2023 08:01:07 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35550 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241310AbjAMNA1 (ORCPT ); Fri, 13 Jan 2023 08:00:27 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 59D8B87F2A; Fri, 13 Jan 2023 04:46:24 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=Sender:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-Id:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description; bh=1DUb3B7waW5odEw04POoGMWila232+t7SZb2vjo28Us=; b=J9D0BI8dDExb7i3ZX/1BsCrR29 veSqoJ+6VcD7dyaYv3NABXoY/CxEv6JnNcLBLtzQdnPwqzzco20zJM/3/Qy0ZEYd5f68ImSQAYbX4 RgfLGUsbIRywulWBLTra7BDQWewHjL7+g6gAztAn+QopRPyw51nY5odgYV/JtsJ9vxnfr5H9po/NN mKN7yYQ10bSCrdQxkPOxTPFjacYPAKDA19GIBhouNVyY4H5ByXfp2uIvK7T51ZA+DButc3iraobBG x+UYkj2TXU9zNpFMvxjL+DAUionlpCsyfvIQWJWfAbcOeEi67pNvOadXYiwPs/OvqFEFMKHJJrDfr ye4nFsXQ==; Received: from i7.infradead.org ([2001:8b0:10b:1:21e:67ff:fecb:7a92]) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1pGJRy-0065y3-Tb; Fri, 13 Jan 2023 12:46:27 +0000 Received: from dwoodhou by i7.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1pGJRl-0002jj-Fy; Fri, 13 Jan 2023 12:46:13 +0000 From: David Woodhouse To: Boqun Feng , linux-kernel@vger.kernel.org, rcu@vger.kernel.org, kvm@vger.kernel.org Cc: Peter Zijlstra , Ingo Molnar , Will Deacon , Waiman Long , Lai Jiangshan , "Paul E . McKenney" , Josh Triplett , Steven Rostedt , Mathieu Desnoyers , David Woodhouse , Paolo Bonzini , seanjc@google.com, Joel Fernandes , Matthew Wilcox , Michal Luczaj Subject: [PATCH 1/3] KVM: Show lockdep the kvm->mutex vs. kvm->srcu ordering rule Date: Fri, 13 Jan 2023 12:46:04 +0000 Message-Id: <20230113124606.10221-2-dwmw2@infradead.org> X-Mailer: git-send-email 2.35.3 In-Reply-To: <20230113124606.10221-1-dwmw2@infradead.org> References: <20230113065955.815667-1-boqun.feng@gmail.com> <20230113124606.10221-1-dwmw2@infradead.org> MIME-Version: 1.0 Sender: David Woodhouse X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org. See http://www.infradead.org/rpr.html Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org From: David Woodhouse Lockdep is learning to spot deadlocks with sleepable RCU vs. mutexes, which can occur where one code path calls synchronize_scru() with a mutex held, while another code path attempts to obtain the same mutex while in a read-side section. Since lockdep isn't very good at reading the English prose in Documentation/virt/kvm/locking.rst, give it a demonstration by calling synchronize_scru(&kvm->srcu) while holding kvm->lock in kvm_create_vm(). The cases where this happens naturally are relatively esoteric and may not happen otherwise. Signed-off-by: David Woodhouse --- virt/kvm/kvm_main.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 13e88297f999..285b3c5a6364 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1173,6 +1173,16 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname) if (init_srcu_struct(&kvm->irq_srcu)) goto out_err_no_irq_srcu; +#ifdef CONFIG_LOCKDEP + /* + * Ensure lockdep knows that it's not permitted to lock kvm->lock + * from a SRCU read section on kvm->srcu. + */ + mutex_lock(&kvm->lock); + synchronize_srcu(&kvm->srcu); + mutex_unlock(&kvm->lock); +#endif + refcount_set(&kvm->users_count, 1); for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) { for (j = 0; j < 2; j++) {