From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8C248C4332F for ; Wed, 23 Nov 2022 20:19:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239355AbiKWUTB (ORCPT ); Wed, 23 Nov 2022 15:19:01 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41634 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239170AbiKWUSl (ORCPT ); Wed, 23 Nov 2022 15:18:41 -0500 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 486248CB8A; Wed, 23 Nov 2022 12:18:32 -0800 (PST) Message-ID: <20221123201306.823305113@linutronix.de> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1669234710; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc; bh=o8uOQEGEwvYxhWAaMgeou6hbxri/lpOsubwv/Uf38Z0=; b=COYcMAmIbivJBidbwe5beja4+qO+a8aJL86E1O0/FC6ijE5U4SgaE/VYSfjK4v7VfrER/J M4MstFRQiuExyavyhsazBJbyu+2tFMasg5J6K2w6oi/OsbbAzRgb8qMwL5wU68MrHpcypC a/Nvi55H+MhuHqZkybiRUsEzuljxPjl3ERCezh2xJQVERdFWebqYjomIfazUdve5gRYFSA RiN2gkIN3/kB08rJU/bbijrSpJxM9kNP8ihnMFPOZpdhFPMsUPm7i//XZUbTY1fAPNqhy7 La6O7XCVTG67CO/ivKTpbhr744TC66Yj9zAp0GAQxonXXREmYwdutqyDhNHt5w== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1669234710; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc; bh=o8uOQEGEwvYxhWAaMgeou6hbxri/lpOsubwv/Uf38Z0=; b=tWkPr6RffzWLQkTR/NQ0KmNfRRYOB5CnJ78EApPCdOd2hKEEecFYpI3ioY7Zg39XeXnDkQ gfsHlazd7+HNAdAQ== From: Thomas Gleixner To: LKML Cc: Linus Torvalds , Steven Rostedt , Anna-Maria Behnsen , Peter Zijlstra , Stephen Boyd , Guenter Roeck , Andrew Morton , Julia Lawall , Arnd Bergmann , Viresh Kumar , Marc Zyngier , Marcel Holtmann , Johan Hedberg , Luiz Augusto von Dentz , linux-bluetooth@vger.kernel.org, "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , netdev@vger.kernel.org, Jacob Keller Subject: [patch V3 00/17] timers: Provide timer_shutdown[_sync]() Date: Wed, 23 Nov 2022 21:18:29 +0100 (CET) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is the third version of the timer shutdown work. The second version can be found here: https://lore.kernel.org/all/20221122171312.191765396@linutronix.de Tearing down timers can be tedious when there are circular dependencies to other things which need to be torn down. A prime example is timer and workqueue where the timer schedules work and the work arms the timer. Steven and the Google Chromebook team ran into such an issue in the Bluetooth HCI code. Steven suggested to create a new function del_timer_free() which marks the timer as shutdown. Rearm attempts of shutdown timers are discarded and he wanted to emit a warning for that case: https://lore.kernel.org/all/20220407161745.7d6754b3@gandalf.local.home This resulted in a lengthy discussion and suggestions how this should be implemented. The patch series went through several iterations and during the review of the last version it turned out that this approach is suboptimal: https://lore.kernel.org/all/20221110064101.429013735@goodmis.org The warning is not really helpful because it's entirely unclear how it should be acted upon. The only way to address such a case is to add 'if (in_shutdown)' conditionals all over the place. This is error prone and in most cases of teardown like the HCI one which started this discussion not required all. What needs to prevented is that pending work which is drained via destroy_workqueue() does not rearm the previously shutdown timer. Nothing in that shutdown sequence relies on the timer being functional. The conclusion was that the semantics of timer_shutdown_sync() should be: - timer is not enqueued - timer callback is not running - timer cannot be rearmed Preventing the rearming of shutdown timers is done by discarding rearm attempts silently. As Steven is short of cycles, I made some spare cycles available and reworked the patch series to follow the new semantics and plugged the races which were discovered during review. The patches have been split up into small pieces to make review easier and I took the liberty to throw a bunch of overdue cleanups into the picture instead of proliferating the existing state further. The last patch in the series addresses the HCI teardown issue for real. The series is also available from git: git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git timers Changes vs. V2: - Fixed up change logs and comments (Anna-Maria) - Picked up Reviewed-by tags Thanks, tglx --- Documentation/RCU/Design/Requirements/Requirements.rst | 2 Documentation/core-api/local_ops.rst | 2 Documentation/kernel-hacking/locking.rst | 17 Documentation/timers/hrtimers.rst | 2 Documentation/translations/it_IT/kernel-hacking/locking.rst | 14 Documentation/translations/zh_CN/core-api/local_ops.rst | 2 arch/arm/mach-spear/time.c | 8 drivers/bluetooth/hci_qca.c | 10 drivers/char/tpm/tpm-dev-common.c | 4 drivers/clocksource/arm_arch_timer.c | 12 drivers/clocksource/timer-sp804.c | 6 drivers/staging/wlan-ng/hfa384x_usb.c | 4 drivers/staging/wlan-ng/prism2usb.c | 6 include/linux/timer.h | 35 kernel/time/timer.c | 425 +++++++++--- net/sunrpc/xprt.c | 2 16 files changed, 405 insertions(+), 146 deletions(-)