From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 500E923F40D for ; Thu, 11 Sep 2025 20:35:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=13.77.154.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757622931; cv=none; b=HhT+Xb69Fy4xOfcSEQefi9Nx3tOzsz3m1bISNwynsdhMcVk/dhWuk/7oYIUADBA5gk7+EdyGp3HR3slpbJq9YjvXInuqkspKfftoJVE0SL5duqxgFp3SmmP6+QQqSQRaJMwxklrS/qmuWmGf7wM8TjEuAygNpthytzk5XIT1nEs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757622931; c=relaxed/simple; bh=yFNSilNHL8JuECHouCrZpRSMJcwNfp6ZFDROPRhkbfg=; h=Message-ID:Date:MIME-Version:From:Subject:To:Content-Type; b=BUjBVwt6ZrdLEskCTwp3TVTgOjbjQadIcRrPKNgcchWREht2LW880IzGLkK5b0XRfAMFzx0ikbiVTqrIb19haynqPMZbwMwyTdp+1vSfWcYT+2/jjFrUARIrT5CvmlCqb1HsR0+/3RgK8lKCq5JZvNW7X6RW+xejLafro5E333s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com; spf=pass smtp.mailfrom=linux.microsoft.com; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b=K+g+U+5w; arc=none smtp.client-ip=13.77.154.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b="K+g+U+5w" Received: from [10.131.143.15] (unknown [167.220.82.15]) by linux.microsoft.com (Postfix) with ESMTPSA id 8CDEB2110801 for ; Thu, 11 Sep 2025 13:35:29 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 8CDEB2110801 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1757622929; bh=b+5Ob1LblBDvQPzZVL9dVWH6v22GKN3EgjOSS1/Slpg=; h=Date:From:Subject:To:From; b=K+g+U+5wgUEarfzc9rRzGWPl9VOBgRjvs3H0In6yktFoKV1Kp6hdXLW9eYG+eEd7A syqRsGTxX+o3g0MSpa5GfjtQZhtvdYhquRrKnaE/PSKZreaMPUFt+xQNflgNpgtNe9 t8O+uO8LnGNDo/SMoL24cpuFrwETQQuEuAB29eac= Message-ID: <38f790d0-aae5-467f-bb1e-c7bd33ddffe7@linux.microsoft.com> Date: Thu, 11 Sep 2025 13:35:33 -0700 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: Tahera Fahimi Subject: Backport rcu-tasks fix to stable kernel version 6.6.y To: stable@vger.kernel.org Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Dear Stable Kernel Maintainers, I am writing to request the backport of the following patches to stable kernel versions 6.6.y, addressing a deadlock issue in RCU Tasks related to do_exit() on preemptible systems. Issue Description: The kernel may experience deadlocks due to shared locking between exit_tasks_rcu_start() and rcu_tasks_postscan() via synchronize_srcu(), when multiple processes exit concurrently. The problem manifests as stalls in the RCU tasks grace period. This issue manifest as a deadlock in WSL kernel which uses the stable kernel 6.6.87 (Please see the issue on https://github.com/microsoft/WSL/issues/13480) Patches to Apply: Patch 1: Subject: rcu-tasks: Maintain lists to eliminate RCU-tasks/do_exit() deadlocks Commit ID: 6b70399f9ef3809f6e308fd99dd78b072c1bd05c Justification: Introduces per-CPU lists for exiting tasks, replacing SRCU-based waits and eliminating deadlocks during concurrent exits. Patch 2: Subject: rcu-tasks: Eliminate deadlocks involving do_exit() and RCU tasks Commit ID: 1612160b91272f5b1596f499584d6064bf5be794 Justification: Ensures all exiting tasks are properly gathered and synchronized, preventing missed synchronizations and further deadlocks. Patch 3: Subject: rcu-tasks: Maintain real-time response in rcu_tasks_postscan() Commit ID: 0bb11a372fc8d7006b4d0f42a2882939747bdbff Justification: Periodically enables interrupts during per-CPU list traversal to maintain system responsiveness, especially when many tasks are present. Kernel version: latest kernel version in 6.6.y branch Thank you for your consideration. Best regards, Tahera Fahimi