From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BA5382D7DDB; Sat, 7 Mar 2026 09:01:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772874084; cv=none; b=b0yK/Yoh0AgtfmWprE1hlzDGKi6HZeNMtYqrR+XqjCE4JZm+TmOQiQ3+ryhYaH/4pSEdRG8ArKx22nEF7zj5Hf7zWQ3MjNkj+YcZJVOTcShpmgzbmGR6fImlzyrutZDBFM8oerFAbdinPlk1Ngh9C0u6RofgKR5/mJ9FhPRAERs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772874084; c=relaxed/simple; bh=HcmWURFUVniNjlOMNWDM3XuhFZvHHR6RnWvZS7kjD5g=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=cgC0XiE/KIS/sIom+nhQ9O67RTcPx0/BltWo+oliK10g/b+EmbTtUXOApmuMqXRrHi7lX6GRb6rF9X7hykWGg1BWvV3LGjalY26UCIP323ySlF8suClXMQAZPa/ej4xtHOmuHvdTliJJHFMbPhpZ+bBvKS9QqOUTOlnTlqAhUwI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=hA+HFpjo; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="hA+HFpjo" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7DE6BC19422; Sat, 7 Mar 2026 09:01:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772874084; bh=HcmWURFUVniNjlOMNWDM3XuhFZvHHR6RnWvZS7kjD5g=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=hA+HFpjozgXqTlDFB0SU/ogBf+NmAVfr8Cd/grcE/wxMp2i/Tr62Z9AxK1wOAcLkR asV19eEDOIcIdV4fmUvFHZhSkygR6E/mBuD0ZWkX+TARAC0xfnygdvSO82yJuHBUmc uqc/Fi+ihn4doL60XgJq0qXoR767rhw/wUG81QAH6g8/c7VZCYFRwRK/y2PssMB/Pd rrY5xqnVOlW4egEBDYjFo6Yz+qIL0/T4GjiUVuj6QsvArog9MuxIImTasX/DGu0Kl+ Iobi7xCHzAav2fDVfrw9As91C4zs/bQmofRtnLXH+K/eV/0CpbMBfJyX0Ieg4aJTvu JtxU+kcF3Amog== From: Thomas Gleixner To: Peter Zijlstra Cc: Jiri Slaby , Matthieu Baerts , Stefan Hajnoczi , Stefano Garzarella , kvm@vger.kernel.org, virtualization@lists.linux.dev, Netdev , rcu@vger.kernel.org, MPTCP Linux , Linux Kernel , Shinichiro Kawasaki , "Paul E. McKenney" , Dave Hansen , "luto@kernel.org" , Michal =?utf-8?Q?Koutn=C3=BD?= , Waiman Long , Marco Elver Subject: Re: Stalls when starting a VSOCK listening socket: soft lockups, RCU stalls, timeout In-Reply-To: <20260306152458.GT606826@noisy.programming.kicks-ass.net> References: <863a5291-a636-47d0-891c-bb0524d2e134@kernel.org> <20260302114636.GL606826@noisy.programming.kicks-ass.net> <717310d8-6274-4b7f-8a19-561c45f5f565@kernel.org> <87zf4m2qvo.ffs@tglx> <47cba228-bba7-4e58-a69d-ea41f8de6602@kernel.org> <87tsuu2i59.ffs@tglx> <7efde2b5-3b72-4858-9db0-22493d446301@kernel.org> <87qzpx2sck.ffs@tglx> <20260306152458.GT606826@noisy.programming.kicks-ass.net> Date: Sat, 07 Mar 2026 10:01:20 +0100 Message-ID: <87ldg42eu7.ffs@tglx> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On Fri, Mar 06 2026 at 16:24, Peter Zijlstra wrote: > On Fri, Mar 06, 2026 at 10:57:15AM +0100, Thomas Gleixner wrote: > >> I tried with tons of test cases which stress test mmcid with threads and >> failed. > > Are some of those in tools/testing/selftests ? > > Anyway, I was going over that code, and I noticed that there seems to be > inconsistent locking for mm_mm_cid::pcpu. > > There's a bunch of sites that state we need rq->lock for remote access; > but then things like sched_mm_cid_fork() and sched_mm_cid_exit() seem to > think that holding mm_cid->lock is sufficient. > > This doesn't make sense to me, but maybe I missed something. fork() and exit() are fully serialized. There can't be a mode change with remote access going on concurrently. I gave up staring at it yesterday as my brain started to melt. Let me try again. Thanks, tglx