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 B3D76C433F5 for ; Mon, 23 May 2022 13:21:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236140AbiEWNVX (ORCPT ); Mon, 23 May 2022 09:21:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35314 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236160AbiEWNVN (ORCPT ); Mon, 23 May 2022 09:21:13 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D2FC063DE for ; Mon, 23 May 2022 06:21:12 -0700 (PDT) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id CDF3A21AD6; Mon, 23 May 2022 13:21:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1653312070; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type; bh=ewYw1fRxVPzaahbUqFNs5STtZWay9ceigZCWA51wXME=; b=J5zwYsGflaUsl4B6PY4vfyuGwRyQ3hR4LH0PNF3GLk4MwilRuPFQnqp32ms6P1PL5R9Dep 9WV8zjlw/DeWcVE5LhQslKdA9w3X8wKARwdlVa4Mio/pMPAsWVj5niCC9yZZ32q6BrwPTt f4O5FLAnzAj85rX9O6cR1UejKi/ypCI= Received: from suse.cz (unknown [10.100.201.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 682362C141; Mon, 23 May 2022 13:21:10 +0000 (UTC) Date: Mon, 23 May 2022 15:21:07 +0200 From: Petr Mladek To: Linus Torvalds Cc: Sergey Senozhatsky , Steven Rostedt , John Ogness , Andy Shevchenko , Rasmus Villemoes , Jan Kara , Peter Zijlstra , linux-kernel@vger.kernel.org Subject: [GIT PULL] printk for 5.19 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Linus, please pull the latest printk changes from git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux.git tags/printk-for-5.19 ================================================ - Offload writing printk() messages on consoles to per-console kthreads. It prevents soft-lockups when an extensive amount of messages is printed. It was observed, for example, during boot of large systems with a lot of peripherals like disks or network interfaces. It prevents live-lockups that were observed, for example, when messages about allocation failures were reported and a CPU handled consoles instead of reclaiming the memory. It was hard to solve even with rate limiting because it would need to take into account the amount of messages and the speed of all consoles. It is a must to have for real time. Otherwise, any printk() might break latency guarantees. The per-console kthreads allow to handle each console on its own speed. Slow consoles do not longer slow down faster ones. And printk() does not longer unpredictably slows down various code paths. There are situations when the kthreads are either not available or not reliable, for example, early boot, suspend, or panic. In these situations, printk() uses the legacy mode and tries to handle consoles immediately. - Add documentation for the printk index. =============================================== Risk: There was always fear that messages might not reach the console when the kthreads could not be scheduled. It blocked introducing the kthreads for nearly a decade. It is clear that the kthreads adds some risk that the messages will not reach consoles. But the original solution was just the best effort either. The kthreads fix some real bugs as mentioned above. Also they allow to see the messages on other consoles when other consoles are slow or get stuck. The patchset has been in linux-next for nearly one month since April 26. It helped to find one already existing race when initializing a console device. It made the race more visible, see https://lore.kernel.org/r/20220508103547.626355-1-john.ogness@linutronix.de Nobody reported problems with missing messages. Of course, it just a good sign but it is not proof of anything. Let's see how it works when it gets more testing in the mainline. I am afraid that we won't find without trying. ---------------------------------------------------------------- Chris Down (1): MAINTAINERS: Add printk indexing maintainers on mention of printk_index John Ogness (15): printk: rename cpulock functions printk: cpu sync always disable interrupts printk: add missing memory barrier to wake_up_klogd() printk: wake up all waiters printk: wake waiters for safe and NMI contexts printk: get caller_id/timestamp after migration disable printk: call boot_delay_msec() in printk_delay() printk: add con_printk() macro for console details printk: refactor and rework printing logic printk: move buffer definitions into console_emit_next_record() caller printk: add pr_flush() printk: add functions to prefer direct printing printk: add kthread console printers printk: extend console_lock for per-console locking printk: remove @console_locked Marco Elver (1): printk, tracing: fix console tracepoint Petr Mladek (2): printk/index: Printk index feature documentation Merge branch 'rework/kthreads' into for-linus Documentation/core-api/index.rst | 1 + Documentation/core-api/printk-index.rst | 137 ++++ MAINTAINERS | 2 + drivers/tty/sysrq.c | 2 + include/linux/console.h | 19 + include/linux/printk.h | 82 ++- kernel/hung_task.c | 11 +- kernel/panic.c | 4 + kernel/printk/printk.c | 1205 +++++++++++++++++++++++-------- kernel/rcu/tree_stall.h | 2 + kernel/reboot.c | 14 +- kernel/watchdog.c | 4 + kernel/watchdog_hld.c | 4 + lib/dump_stack.c | 4 +- lib/nmi_backtrace.c | 4 +- 15 files changed, 1174 insertions(+), 321 deletions(-) create mode 100644 Documentation/core-api/printk-index.rst