From mboxrd@z Thu Jan 1 00:00:00 1970 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 10E44C6FD1C for ; Fri, 24 Mar 2023 23:13:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229605AbjCXXNo (ORCPT ); Fri, 24 Mar 2023 19:13:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41460 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232019AbjCXXNl (ORCPT ); Fri, 24 Mar 2023 19:13:41 -0400 Received: from mail-pj1-x104a.google.com (mail-pj1-x104a.google.com [IPv6:2607:f8b0:4864:20::104a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 44A1A15CB8 for ; Fri, 24 Mar 2023 16:13:39 -0700 (PDT) Received: by mail-pj1-x104a.google.com with SMTP id o89-20020a17090a0a6200b0023b3d3acdd6so2853805pjo.3 for ; Fri, 24 Mar 2023 16:13:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; t=1679699619; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=DcyHkCN+ppZSMBTdximdTt+L7x4aLTNRaJDAdNPZ4ng=; b=odSJ3ACgQqEJX3WSsVrtBVvR1cKZSOG86JAwa9zIOtfifrGXyxzSrkZIWbTOzMbu7+ kNrnCnvLyIzEiZIn+Wloa9/qENdDRtszbDrcIpQcQzom1LgeABvbxo07uQGQt+XZ8fNe OM5pCRDA0AFxNh2TTh+oN9UEukp7X5/2PISXhBT0MVP9nolVA3gYAah4zbA+J3PytKWm QfUCKQjSK8lDzkeS6+o23xNKzRBp0/1nkwX4g4QCDJ6Ot2Pda7aTMu1/Mzwr4+ztFbdE pRwQQApJ27OMld307ob6SYfmLDyo4e94r6/tb/WueOovi0nSl2KY5GIfNyEQTDCXsjZL 4gqw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1679699619; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=DcyHkCN+ppZSMBTdximdTt+L7x4aLTNRaJDAdNPZ4ng=; b=0yVb12E/s+EufnbNXfB3R0npWo5kzTsylKLoF0pyjn5nDiVK6trdChCmEyP+jLFlsT 1j0yPebR5pSqsQfY+C2QgLbU1ODHAdZu08OOUPI6ys+g/v3kZe8vMbPHQYgXLOXkQft3 CVCQgSMcBFmows96WYH/5o3Z2yR/FBttULWwwNfpCHDRpzlI77IzU0BM4WgosVIO5R54 usuvCPA78UZ3Jh7LU6On73hBf7RWsDZRra/JnhWHwY76DC88H8+JHBQhQaU7vS8yFDZm D3nMyWBbtIyULEWxqnblq1NnCSRvsyhgM7+wMqYRILnL/WxvWBSJ7quKWEh/1jGiQrt9 aMSQ== X-Gm-Message-State: AAQBX9ecuIZLLwTnig5FRcBNnoLIlW2zc0mEBmoYTQbxHhFCRgvoy4bn UMo7auCp880S30VQbuxcsoHj0F9Cd8A= X-Google-Smtp-Source: AK7set9poMEJJGCyeA2Pj8j7Kdn85X08yTBcBCvExVQxc0PKno5Jvma2+GhBaotZP4G93ZVxxwOcGaUPX90= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a05:6a00:2313:b0:626:23a1:7b9d with SMTP id h19-20020a056a00231300b0062623a17b9dmr2342573pfh.6.1679699618843; Fri, 24 Mar 2023 16:13:38 -0700 (PDT) Date: Fri, 24 Mar 2023 16:13:37 -0700 In-Reply-To: <20230313111022.13793-1-yan.y.zhao@intel.com> Mime-Version: 1.0 References: <20230313111022.13793-1-yan.y.zhao@intel.com> Message-ID: Subject: Re: [PATCH v3] KVM: VMX: fix lockdep warning on posted intr wakeup From: Sean Christopherson To: Yan Zhao Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com Content-Type: text/plain; charset="us-ascii" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 13, 2023, Yan Zhao wrote: > The lock ordering after this patch are: > - &p->pi_lock --> &rq->__lock --> > &per_cpu(wakeup_vcpus_on_cpu_lock_out, cpu) > - &per_cpu(wakeup_vcpus_on_cpu_lock_in, cpu) --> > &per_cpu(wakeup_vcpus_on_cpu_lock_out, cpu) > - &per_cpu(wakeup_vcpus_on_cpu_lock_in, cpu) --> &p->pi_lock > > Currently, &rq->__lock is not held in "path sched_in". > However, if in future "path sched_in" takes &p->pi_lock or &rq->__lock, > lockdep is able to detect and warn in that case. > > Signed-off-by: Yan Zhao > [sean: path sched_out and path irq does not race, path sched_in does not > take &rq->__lock] But there's no actual deadlock, right? I have zero interest in fixing a lockdep false positive by making functional changes to KVM. I am definitely open to making changes to somehow let lockdep know what's going on, but complicating KVM's actual functionality is too much.