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 4940A369998 for ; Wed, 11 Mar 2026 09:43:18 +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=1773222198; cv=none; b=KfWprqjoHwRIvPRQ7ChXP3s3gbgHnO3WxUL1ck6v6CAM/t1ofb24V98QIc6SBn3smeHAu7qG8AgOHg7giN5quXjuc8pWselQo3pophNAUWXlxkfbyKeucFf6oj15gW2Ny55tY/GSdVZo10F1W9lPnXOj2Slgh9LIYb+qeqSDfnY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773222198; c=relaxed/simple; bh=S63G8lfSfgvwAMhMQm06DSfuNS6GGE01szX2H74AMFQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=IcIwJghjpKpMFKzZKx+GkR1oHegR+Hz52trz7WfqOBweN3MtUsTdQzr3Ma6Spj+vog8WRSQ5pzeo2KFslmbjNorJJkJqfe4f7XqeaEEL8/0UaZ1vN6AZ05g5z1a3axxGEeWoymlZarDxrT4NqDC48kA0cOiqYOh2Mrebq6Yd+kY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=fczJr0x6; 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="fczJr0x6" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CE9EBC2BC86; Wed, 11 Mar 2026 09:43:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773222198; bh=S63G8lfSfgvwAMhMQm06DSfuNS6GGE01szX2H74AMFQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=fczJr0x64T5wMHh8nHG3LZxL1ZdNn28V0VB32WPrJpoATlVghX+icIxm5bpRCCx3d 2cLr0DqUr894FDjEgXyATkkCW+opDP0ue6hJzjYY795HvuWkx62wg97ZsXCh7vdj7B Fxuzc9Mi2BxfMt58jVRJHTEVhKHAf9utnfltZ4e2Kk74NS51Xn7K0kN3tmf4NOEuip jMc66Jtf1s0wFVoQh5HMD1Pjet+I6zeEFqkfZTT63SA5xz2QCbwXUzNsSpAQt8Ex9H EGBzVOJGiLc2HfLcpTDeQHX8KZ8COXmBHyHBFMRGvHCjF4e+UDIaNS/1qPFpDFAQ8A tgv6BmrSnas/g== Message-ID: <314e3ad8-4912-4c37-bf35-988b99f5a816@kernel.org> Date: Wed, 11 Mar 2026 10:43:14 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Beta Subject: Re: [patch 0/4] sched/mmcid: Cure fork()/vfork() related problems Content-Language: fr To: Thomas Gleixner , LKML Cc: Peter Zijlstra , Mathieu Desnoyers , Jiri Slaby References: <20260310201009.257617049@kernel.org> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Thomas, On 10/03/2026 21:28, Thomas Gleixner wrote: > Matthiue and Jiri reported CPU stalls where a CPU git stuck in mm_get_cid(): > > https://lore.kernel.org/b24ffcb3-09d5-4e48-9070-0b69bc654281@kernel.org > > After some tedious debugging it turned out to be another subtle (or not so > subtle) ownership mode change issue. > > The logic handling vfork()'ed tasks in sched_mmcid_fixup_tasks_to_cpus() is > broken. It is invoked when the number of tasks associated to a process is > smaller than the number of MMCID users. It then walks the task list to find > the vfork()'ed task, but accounts all the already processed tasks as well. > > If that double processing brings the number of to be handled tasks to 0, > the walk stops and the vfork()'ed task's CID is not fixed up. As a > consequence a subsequent schedule in fails to acquire a (transitional) CID > and the machine stalls. > > Peter and me discovered also that there is a yet unreported issue > vs. concurrent forks. Jiri noticed it independently. > > The following series fixes those issues. It applies on top of Linus tree. Thank you for this series! My CI also complained about the missing "#ifdef CONFIG_SCHED_MM_CID" with "make tinyconfig", but for the rest, I didn't have any issues to boot 200 times! Just in case you need this tag: Tested-by: Matthieu Baerts (NGI0) Cheers, Matt -- Sponsored by the NGI0 Core fund.