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 25989C07E96 for ; Thu, 15 Jul 2021 04:14:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F36AD610C7 for ; Thu, 15 Jul 2021 04:14:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235112AbhGOERm (ORCPT ); Thu, 15 Jul 2021 00:17:42 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:37318 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233862AbhGOERl (ORCPT ); Thu, 15 Jul 2021 00:17:41 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1626322488; 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=46nqW8DAvxZ4d9NOPpXHF/nyKumPjQmdJUEBZ822R6k=; b=hnxTSyrR5EAHagS8WM21NptdGjqt2Slduil6A2D7Qqk+T7txpNcNj6S1HpfHdxxkdIFZSX Z2PqWRNmu6pK4VjlSCr0B1OVJf9hD9K7CUPsxEhFaqFTOUFsbvc4ZRCXqWF8FaCDBBIfns tgGICR0vRme3jIc3lIxvJ0ne0LYzsT4= 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-297-9gIjh7emMqq05rwfSsf5uw-1; Thu, 15 Jul 2021 00:14:46 -0400 X-MC-Unique: 9gIjh7emMqq05rwfSsf5uw-1 Received: by mail-pg1-f200.google.com with SMTP id x9-20020a6541490000b0290222fe6234d6so3373548pgp.14 for ; Wed, 14 Jul 2021 21:14:46 -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=46nqW8DAvxZ4d9NOPpXHF/nyKumPjQmdJUEBZ822R6k=; b=ptOZBZQB6tXGFLDI4CxIFMLTvSXWW6qCCQdJVLizN8SJtNLGBdRPCoSnkC41VxAeo0 /Q88Y4vZ/qjRgDyljs3uAOoj4g3HSLi3pQjoLdLbSDMcyqh6vYjvjWyZ1IdSuw/dzsIo kL2usI0ilfTXhwuraNl2YYMnlucX3gzLIotYcExxDMJ9oStBFyV9HfIa4QFwwHdhUukx cYTGVDEzOsU0z8zLR9UAW8Ew4VvWGYl+Jqt5o+uGUO2lIgwbwevGGFLu/FTAh4tkI+2+ z1roicwFXP4G9f3rC2YO7WJDtVmQ9Tc515hzBLJNPsA6Jm1Ns2VYs3NdEVVxhR2anEOD 4LIw== X-Gm-Message-State: AOAM531OqcYQ/e6OWvJaF4Fs7NjHzWG/hOMHR2OgPNq/Xx7v8YpiJNDJ HMVnQtUhUH13eIzk27610KpUJ7w9qy41kte4SXL26iAa8nPHHXzURcbdKAV2rUUzPrzNcmRZ1b8 slfyUdaSYy2CtUeKxJEv9vuE4 X-Received: by 2002:a17:902:d652:b029:12b:45c1:21ba with SMTP id y18-20020a170902d652b029012b45c121bamr1585587plh.9.1626322485781; Wed, 14 Jul 2021 21:14:45 -0700 (PDT) X-Google-Smtp-Source: ABdhPJznF+pXe4rDHrMmM9hW4X2YwNPTYLHbnR9mjaMrfItnzAt+oi7sJGE+qjAS68FBStfC98NNDg== X-Received: by 2002:a17:902:d652:b029:12b:45c1:21ba with SMTP id y18-20020a170902d652b029012b45c121bamr1585562plh.9.1626322485447; Wed, 14 Jul 2021 21:14:45 -0700 (PDT) Received: from wangxiaodeMacBook-Air.local ([209.132.188.80]) by smtp.gmail.com with ESMTPSA id x6sm5177267pgq.67.2021.07.14.21.14.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 14 Jul 2021 21:14:44 -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> From: Jason Wang Message-ID: <4b53e2be-c38e-7509-dfcf-94f5bf5dcc10@redhat.com> Date: Thu, 15 Jul 2021 12:14:36 +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: <475f84e2-78ee-1a24-ef57-b16c1f2651ed@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 2021/7/14 下午6:35, Paolo Bonzini 写道: > On 14/07/21 11:23, Jason Wang wrote: >>> This was added in 2020, so it's unlikely to be the direct cause of the >>> change.  What is a known-good version for the host? >>> >>> Since it is not KVM stuff, I'm CCing Michael and Jason. >> >> I think this can be probably fixed here: >> >> https://lore.kernel.org/lkml/20210618084412.18257-1-zhe.he@windriver.com/ >> > > That seems wrong; in particular it wouldn't protect against AB/BA > deadlocks. > In fact, the bug is with the locking; the code assumes that > spin_lock_irqsave/spin_unlock_irqrestore is non-preemptable and therefore > increments and decrements the percpu variable inside the critical > section. > > This obviously does not fly with PREEMPT_RT; the right fix should be > using a local_lock.  Something like this (untested!!): > > --------------- 8< --------------- > From: Paolo Bonzini > Subject: [PATCH] eventfd: protect eventfd_wake_count with a local_lock > > eventfd_signal assumes that spin_lock_irqsave/spin_unlock_irqrestore is > non-preemptable and therefore increments and decrements the percpu > variable inside the critical section. > > 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. 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; >  } >