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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id e7sm14027593edk.3.2021.07.26.04.03.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 26 Jul 2021 04:03:16 -0700 (PDT) To: Hillf Danton Cc: Thomas Gleixner , Sebastian Andrzej Siewior , "Michael S. Tsirkin" , linux-mm@kvack.org, LKML , Al Viro References: <8dfc0ee9-b97a-8ca8-d057-31c8cad3f5b6@redhat.com> <475f84e2-78ee-1a24-ef57-b16c1f2651ed@redhat.com> <20210715102249.2205-1-hdanton@sina.com> <20210716020611.2288-1-hdanton@sina.com> <20210716075539.2376-1-hdanton@sina.com> <20210716093725.2438-1-hdanton@sina.com> <20210718124219.1521-1-hdanton@sina.com> <20210721070452.1008-1-hdanton@sina.com> <20210721101119.1103-1-hdanton@sina.com> <20210723022356.1301-1-hdanton@sina.com> <20210723094830.1375-1-hdanton@sina.com> <20210724043320.1654-1-hdanton@sina.com> From: Paolo Bonzini Subject: Re: 5.13-rt1 + KVM = WARNING: at fs/eventfd.c:74 eventfd_signal() Message-ID: Date: Mon, 26 Jul 2021 13:03:15 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210724043320.1654-1-hdanton@sina.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 24/07/21 06:33, Hillf Danton wrote: > lock WQ > count += n > no waiter > unlock WQ Ok, this is a write. > > lock WQ > add waiter for EPOLLIN > unlock WQ This is eventfd_poll(). It hasn't yet returned EPOLLIN. > lock WQ > count = 0 > wakeup EPOLLOUT > unlock WQ This is a read(). > lock WQ > count += n > no waiter > unlock WQ This is wrong; after "unlock WQ" in CPU3 there *is* a waiter, no one has waked it up yet. Paolo > ------------------------------- c1 = count