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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id c15sm1292998wmr.28.2021.07.14.01.10.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 14 Jul 2021 01:10:09 -0700 (PDT) Subject: Re: 5.13-rt1 + KVM = WARNING: at fs/eventfd.c:74 eventfd_signal() To: Daniel Bristot de Oliveira , Thomas Gleixner , Sebastian Andrzej Siewior , "Jason Wang (jasowang@redhat.com)" , "Michael S. Tsirkin" Cc: LKML , Al Viro References: From: Paolo Bonzini Message-ID: <8dfc0ee9-b97a-8ca8-d057-31c8cad3f5b6@redhat.com> Date: Wed, 14 Jul 2021 10:10:08 +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 14/07/21 10:01, Daniel Bristot de Oliveira wrote: > Hey > > I use kvm-vm for regular development, and while using the kernel-rt v5.13-rt1 > (the latest) on the host, and a regular kernel on the guest, after a while, > this happens: > > [ 1723.404979] ------------[ cut here ]------------ > [ 1723.404981] WARNING: CPU: 12 PID: 2554 at fs/eventfd.c:74 eventfd_signal+0x7e/0x90 > [ 1723.405055] RIP: 0010:eventfd_signal+0x7e/0x90 > [ 1723.405059] Code: 01 00 00 00 be 03 00 00 00 4c 89 ef e8 5b ec d9 ff 65 ff 0d e4 34 c9 5a 4c 89 ef e8 ec a8 86 00 4c 89 e0 5b 5d 41 5c 41 5d c3 <0f> 0b 45 31 e4 5b 5d 4c 89 e0 41 5c 41 5d c3 0f 1f 00 0f 1f 44 00 > [ 1723.405078] vhost_tx_batch.constprop.0+0x7d/0xc0 [vhost_net] > [ 1723.405083] handle_tx_copy+0x15b/0x5c0 [vhost_net] > [ 1723.405088] ? __vhost_add_used_n+0x200/0x200 [vhost] > [ 1723.405092] handle_tx+0xa5/0xe0 [vhost_net] > [ 1723.405095] vhost_worker+0x93/0xd0 [vhost] > [ 1723.405099] kthread+0x186/0x1a0 > [ 1723.405103] ? __kthread_parkme+0xa0/0xa0 > [ 1723.405105] ret_from_fork+0x22/0x30 > [ 1723.405110] ---[ end trace 0000000000000002 ]--- The WARN has this comment above: /* * Deadlock or stack overflow issues can happen if we recurse here * through waitqueue wakeup handlers. If the caller users potentially * nested waitqueues with custom wakeup handlers, then it should * check eventfd_signal_count() before calling this function. If * it returns true, the eventfd_signal() call should be deferred to a * safe context. */ 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. Paolo