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 X-Spam-Level: X-Spam-Status: No, score=-18.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5C5E6C07E96 for ; Thu, 15 Jul 2021 06:45:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 341ED61279 for ; Thu, 15 Jul 2021 06:45:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236079AbhGOGsb (ORCPT ); Thu, 15 Jul 2021 02:48:31 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:27371 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231352AbhGOGsa (ORCPT ); Thu, 15 Jul 2021 02:48:30 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1626331537; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Mwi10TZc1sOVU5XYi2wL7hupe8YHyAn6IrGpWJ2vsRw=; b=ZooD0VdhX+sKkrYdtuDT0cZXtzGO4Wq7mu8FkILqaeRpVthkBk5Q2YBVw5PD65axfcDDbk wY6TApcC2n+YoO6it+KO+HtRsvYwBTbwK5c/vYefe0rtEzIosGRRnobrbg2dp3ZpZwzr9o iIvGPjQPAZff4eYe6N+Am9YJSUip78Q= Received: from mail-pg1-f200.google.com (mail-pg1-f200.google.com [209.85.215.200]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-478-zSaansEWO4mrXfN2xw_SNg-1; Thu, 15 Jul 2021 02:45:36 -0400 X-MC-Unique: zSaansEWO4mrXfN2xw_SNg-1 Received: by mail-pg1-f200.google.com with SMTP id 29-20020a63105d0000b029022c245c3492so3630542pgq.17 for ; Wed, 14 Jul 2021 23:45:36 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding :content-language; bh=Mwi10TZc1sOVU5XYi2wL7hupe8YHyAn6IrGpWJ2vsRw=; b=DFSKlZezkHzSENvxY4vVP/nX93XGX6ZKJbRlF/2E6UdWkV+gHqm5iC3dl4UHtbkkd7 8Qgm7cAFsHfY2loyZL5NR/cPsj1mrUYNdZNmTSdnS9REwZxlhJiHmn1131UcUw215Xk+ r8KGzN+Ues1bcuRsA2uQElBjRc7mZnpLQ3FMk7KghqvDvsxChSf13QCiZ6Mm4oPl7a8+ N+2L+W0Lw+zhqanDyk4KDx2rPdaWDq0rezBicXRTYJ5oWHxJ8Ph36Kv19qRGh/jySPIA L8SgJeUEtClpfb8Jbo2EqyY4KRbOr0j8ijSiqFUzyI11KQDeGJ/7Yh3O7iNtFI/vk0/+ n3QA== X-Gm-Message-State: AOAM530LVaBLNjbhmnfwBfsUiwyg4UQuoCP1cKLp7wa/yxw1qGvo858i ynUxDkEGM7SpnLHxVaaxwgwso/uhJO4a9HQAAsoKupsPZbGTiF5F7eZTFKbe7pfE9/udjrJ09ci YRurQx7VJ7agBJdlBmpr2wnsY X-Received: by 2002:a17:90a:a798:: with SMTP id f24mr2785300pjq.8.1626331535202; Wed, 14 Jul 2021 23:45:35 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwfqyK19LEtsygJL/KLKR1mr/sWPJaJdZwDH6P4bSe1nJu+W1HJ8zXJWxL5yx1E1hZaadCZbg== X-Received: by 2002:a17:90a:a798:: with SMTP id f24mr2785283pjq.8.1626331534920; Wed, 14 Jul 2021 23:45:34 -0700 (PDT) Received: from wangxiaodeMacBook-Air.local ([209.132.188.80]) by smtp.gmail.com with ESMTPSA id i12sm4144911pjj.9.2021.07.14.23.45.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 14 Jul 2021 23:45:34 -0700 (PDT) Subject: Re: 5.13-rt1 + KVM = WARNING: at fs/eventfd.c:74 eventfd_signal() To: Paolo Bonzini , Daniel Bristot de Oliveira , Thomas Gleixner , Sebastian Andrzej Siewior , "Michael S. Tsirkin" , Juri Lelli Cc: LKML , Al Viro , He Zhe References: <8dfc0ee9-b97a-8ca8-d057-31c8cad3f5b6@redhat.com> <475f84e2-78ee-1a24-ef57-b16c1f2651ed@redhat.com> <4b53e2be-c38e-7509-dfcf-94f5bf5dcc10@redhat.com> <52348289-5d4d-f4a4-6fe3-f0c24cc6d9f9@redhat.com> From: Jason Wang Message-ID: <987e69e1-21d7-625d-4e45-bc40857a526c@redhat.com> Date: Thu, 15 Jul 2021 14:45:14 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <52348289-5d4d-f4a4-6fe3-f0c24cc6d9f9@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 在 2021/7/15 下午1:58, Paolo Bonzini 写道: > On 15/07/21 06:14, Jason Wang wrote: >>> This obviously does not fly with PREEMPT_RT.  If eventfd_signal is >>> preempted and an unrelated thread calls eventfd_signal, the result is >>> a spurious WARN.  To avoid this, protect the percpu variable with a >>> local_lock. >> >> But local_lock only disable migration not preemption. > > On mainline PREEMPT_RT, local_lock is an array of per-CPU spinlocks. > When two eventfd_signals run on the same CPU and one is preempted, the > spinlocks avoid that the second sees eventfd_wake_count > 0. > > Thanks, > > Paolo Right, I see. Thanks > >> Or anything I missed here? >> >> Thanks >> >> >>> >>> Reported-by: Daniel Bristot de Oliveira >>> Fixes: b5e683d5cab8 ("eventfd: track eventfd_signal() recursion depth") >>> Cc: stable@vger.kernel.org >>> Cc: He Zhe >>> Cc: Jens Axboe >>> Signed-off-by: Paolo Bonzini >>> >>> diff --git a/fs/eventfd.c b/fs/eventfd.c >>> index e265b6dd4f34..7d27b6e080ea 100644 >>> --- a/fs/eventfd.c >>> +++ b/fs/eventfd.c >>> @@ -12,6 +12,7 @@ >>>  #include >>>  #include >>>  #include >>> +#include >>>  #include >>>  #include >>>  #include >>> @@ -25,6 +26,7 @@ >>>  #include >>>  #include >>> >>> +static local_lock_t eventfd_wake_lock = >>> INIT_LOCAL_LOCK(eventfd_wake_lock); >>>  DEFINE_PER_CPU(int, eventfd_wake_count); >>> >>>  static DEFINE_IDA(eventfd_ida); >>> @@ -71,8 +73,11 @@ __u64 eventfd_signal(struct eventfd_ctx *ctx, >>> __u64 n) >>>       * it returns true, the eventfd_signal() call should be >>> deferred to a >>>       * safe context. >>>       */ >>> -    if (WARN_ON_ONCE(this_cpu_read(eventfd_wake_count))) >>> +    local_lock(&eventfd_wake_lock); >>> +    if (WARN_ON_ONCE(this_cpu_read(eventfd_wake_count))) { >>> +        local_unlock(&eventfd_wake_lock); >>>          return 0; >>> +    } >>> >>>      spin_lock_irqsave(&ctx->wqh.lock, flags); >>>      this_cpu_inc(eventfd_wake_count); >>> @@ -83,6 +88,7 @@ __u64 eventfd_signal(struct eventfd_ctx *ctx, >>> __u64 n) >>>          wake_up_locked_poll(&ctx->wqh, EPOLLIN); >>>      this_cpu_dec(eventfd_wake_count); >>>      spin_unlock_irqrestore(&ctx->wqh.lock, flags); >>> +    local_unlock(&eventfd_wake_lock); >>> >>>      return n; >>>  } >>> >> >