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([2001:b07:6468:f312:5e2c:eb9a:a8b6:fd3e]) by smtp.gmail.com with ESMTPSA id b9sm7137793wrh.81.2021.07.15.02.51.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 15 Jul 2021 02:51:34 -0700 (PDT) Subject: Re: 5.13-rt1 + KVM = WARNING: at fs/eventfd.c:74 eventfd_signal() To: He Zhe , Daniel Bristot de Oliveira , Jason Wang , Thomas Gleixner , Sebastian Andrzej Siewior , "Michael S. Tsirkin" , Juri Lelli Cc: LKML , Al Viro References: <8dfc0ee9-b97a-8ca8-d057-31c8cad3f5b6@redhat.com> <475f84e2-78ee-1a24-ef57-b16c1f2651ed@redhat.com> From: Paolo Bonzini Message-ID: Date: Thu, 15 Jul 2021 11:51:32 +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: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 15/07/21 10:44, He Zhe wrote: > It was to increase the recursion depth to 2 so that vhost_worker and > kvm_vcpu_ioctl syscall could work in parallel The count is per-CPU, so parallel operations cannot cause it to become 2. Your patch might fix calls from ioeventfd to vhost_worker to another eventfd, but not *parallel* operation of KVM and vhost (except on PREEMPT_RT). You should identify the exact callstack that caused the warning for vDUSE, and document that one in the commit message, so that reviewers can understand the issue. Paolo