From nobody Fri Sep 19 00:54:51 2025 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 848DBC4321E for ; Wed, 30 Nov 2022 16:20:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229949AbiK3QUX (ORCPT ); Wed, 30 Nov 2022 11:20:23 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41858 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229449AbiK3QUV (ORCPT ); Wed, 30 Nov 2022 11:20:21 -0500 Received: from mail-wr1-x449.google.com (mail-wr1-x449.google.com [IPv6:2a00:1450:4864:20::449]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4196A2B61A for ; Wed, 30 Nov 2022 08:20:19 -0800 (PST) Received: by mail-wr1-x449.google.com with SMTP id t12-20020adfa2cc000000b0022adcbb248bso3681515wra.1 for ; Wed, 30 Nov 2022 08:20:19 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:from:subject:message-id:mime-version:date:from:to:cc:subject :date:message-id:reply-to; bh=e7aXnerOs81qEvUrhkJcE1R45f2KSaCBn6wkFjPKb+E=; b=m0vwX16TqEB4CoFMpCUL9QVzQnd31EsRH55uiPE7Vvc9IDMC0WfSj/YVs1Q5jjc9SU 9J6vMT22Ba0EJbzjviX8PhqKa5B24+Tvg2DTtSW6B+qFw8tXHN7nabGV69R6yDg7xnps FK3lqBa129KX/S7XLocBeMdOMHg6bHdoQNRNwhj3I3sNWXrzS/SyrS0QD+RfLvgqiLkh RvrjWHxrmJcl5SQcsYB2djR1W3qNqltXspeAD1zG3/BRxhLed+NPkAGamLIMX6bw/7ql zK8qIeaQPVQkO74QlJgfANNpKLiZn0UrDvJeKbKe0ccKtyZk3sj3BUhpgI6B2JqRTvmQ 8XXQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=e7aXnerOs81qEvUrhkJcE1R45f2KSaCBn6wkFjPKb+E=; b=BImvvqlT8qK7Orx9ZDniVFbUcG4mWCvdztTgE0BOIiRECzJX6jpyDnkxrqdgLRPtKi 4jF04m8tSY9JuPVis/woy4wNE82ZgAtGjG5osgH/BouUu2CaDuiQdNe4kIbXFVattvf9 nLHMDj/xtUfsv1ewzMswHNrdWpaSdW3BulWbNv8kgvvsFEXdeuN9uP6Lh6pDFRSpme7+ K446M7DXXWgpAtA2xGZFxodbqRzlB+vkdOEsh4XLkrzzfpMmUKpZFkUNcPWl63x5/kBW XtFfyUwm9UFld92UMGSm7rYqxVLWyXjHVfrukWIGqVphxohBtZofwenVjQV2eNyQrw2g MlTA== X-Gm-Message-State: ANoB5pnKUy7FtXKg7N9+ADPMoN/uJWEAOPn/BpF45reTcTqT4LfNAMW7 jo2EzsXkfrAk0iz9L33/PbAh8c8= X-Google-Smtp-Source: AA0mqf41Iqo1Xr4q/u4l0UTpEcPOH4dcv2oiqQGFjNnNGHT8V7/hmhjBp1rBvUhdxCKIQBtV5bUOVnw= X-Received: from corndog.c.googlers.com ([fda3:e722:ac3:cc00:28:9cb1:c0a8:20e0]) (user=spm job=sendgmr) by 2002:a05:6000:1108:b0:235:8867:50bf with SMTP id z8-20020a056000110800b00235886750bfmr28519161wrw.193.1669825217787; Wed, 30 Nov 2022 08:20:17 -0800 (PST) Date: Wed, 30 Nov 2022 16:19:46 +0000 Mime-Version: 1.0 X-Mailer: git-send-email 2.38.1.584.g0f3c55d4c2-goog Message-ID: <20221130161946.3254953-1-spm@google.com> Subject: [PATCH] KVM: Deal with nested sleeps in kvm_vcpu_block() From: Space Meyer To: kvm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: pbonzini@redhat.com, kpsingh@kernel.org, Space Meyer Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Previously this code assumed nothing would mess with current->state between the set_current_state() and schedule(). However the call to kvm_vcpu_check_block() in between might end up requiring locks or other actions, which would change current->state. A similar pattern was described in the "The problem with nested sleeping primitives" LWN article[0]. [0] https://lwn.net/Articles/628628 Signed-off-by: Space Meyer --- virt/kvm/kvm_main.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index fab4d37905785..64e10d73f2a92 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -32,6 +32,7 @@ #include #include #include +#include #include #include #include @@ -3426,6 +3427,7 @@ static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu) */ bool kvm_vcpu_block(struct kvm_vcpu *vcpu) { + DEFINE_WAIT_FUNC(vcpu_block_wait, woken_wake_function); struct rcuwait *wait =3D kvm_arch_vcpu_get_wait(vcpu); bool waited =3D false; =20 @@ -3437,13 +3439,11 @@ bool kvm_vcpu_block(struct kvm_vcpu *vcpu) preempt_enable(); =20 for (;;) { - set_current_state(TASK_INTERRUPTIBLE); - if (kvm_vcpu_check_block(vcpu) < 0) break; =20 waited =3D true; - schedule(); + wait_woken(&vcpu_block_wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT); } =20 preempt_disable(); --=20 2.38.1.584.g0f3c55d4c2-goog