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 0779BC4332F for ; Mon, 6 Nov 2023 21:07:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233098AbjKFVHj (ORCPT ); Mon, 6 Nov 2023 16:07:39 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57694 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229755AbjKFVHi (ORCPT ); Mon, 6 Nov 2023 16:07:38 -0500 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ED2A3A3 for ; Mon, 6 Nov 2023 13:07:34 -0800 (PST) From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1699304852; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=CxVp08tt1OIa0s48HQ/tV2mA7uFrK13yA3t6gp6F8Fc=; b=jX771zxVFdlvVT+BMuix58PggzwWZyGU9AIk+3z4/LqF/wPMLqLYEbiU1DOrt9xuBXxC6f z8fYDP2sz69xCP4lJqziAhnOMwByPKVqGAjWRXER2jgvP+KtRtr7v6zC+j1e6+mbphvnUC D7JWChOti4SIsRSGa2sRt7v+2EZ0eAHPLDM04PRpRqxCHFBs4cAnKwcj8f06/1Zrj7aZG8 uV0qZ+Z+VjiB4fx09ReeigXF58dQ34aAQyyCeELWWvI6iWx4k5kOjwQ+Ack+UMJycWBgs/ wG4k657yyHeJEj+yKzlzwq6MESIPjgY2RlIeBxcFcFssqRq3ltuvE5VilkfvCQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1699304852; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=CxVp08tt1OIa0s48HQ/tV2mA7uFrK13yA3t6gp6F8Fc=; b=E4vluTwmVBlSkyUSiU/AeV5YY09slGF2UYdYAxjL6d3xdgCqg03VFul74xmexa+Q/G7mfs VRdeJvuxHmY9nECg== To: Petr Mladek Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, Mukesh Ojha Subject: [PATCH printk v2 0/9] fix console flushing Date: Mon, 6 Nov 2023 22:13:21 +0106 Message-Id: <20231106210730.115192-1-john.ogness@linutronix.de> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, While testing various flushing scenarios, I stumbled on a couple issues that cause console flushing to fail. While discussing the v1 [0] series, a couple more issues arose. This series addresses all the issues: 1. The prb_next_seq() optimization caused inconsistent return values. Fix prb_next_seq() to the originally intended behavior but keep an optimization. 2. pr_flush() might not wait until the most recently stored printk() message if non-finalized records precede it. Fix pr_flush() to wait for all records to print that are at least reserved at the time of the call. 3. In panic, the panic messages will not print if non-finalized records precede them. Add a special condition so that readers on the panic CPU can drop non-finalized records. 4. It is possible (and easy to reproduce) a scenario where the console on the panic CPU hands over to a waiter of a stopped CPU. Do not use the handover feature in panic. 5. If messages are being dropped during panic, non-panic CPUs are silenced. But by then it is already too late and most likely the panic messages have been dropped. Change the non-panic CPU silencing logic to restrict non-panic CPUs from flooding the ringbuffer. This series also performing some minor cleanups to remove open coded checks about the panic context and improve documentation language regarding data-less records. Because of multiple refactoring done in recent history, it would be helpful to provide the LTS maintainers with the proper backported patches. I am happy to do this. The changes since v1: - Rename NO_LPOS to EMPTY_LINE_LPOS. - Add and cleanup documentation to clarify language regarding data-less records and special lpos values. - Implement a new prb_next_seq() optimization to preserve the intended behavior. This is essentially my rfc [1] with memory barriers added and based on an alternate implemenation suggested by pmladek [2]. - Introduce new prb_next_reserve_seq() function to return the sequence number after @head_id. - Use prb_next_reserve_seq() instead of prb_next_seq() for pr_flush(). - Implement dropping non-finalized records in panic within _prb_read_valid() instead of printk_get_next_message(). This also makes use of the new prb_next_reserve_seq(). - Use the alternate implementation from pmladek [3] to avoid the handover feature in panic. - Implement a new strategy to avoid dropping panic messages when non-panic CPUs are flooding the ringbuffer. John Ogness [0] https://lore.kernel.org/lkml/20231013204340.1112036-1-john.ogness@linutronix.de [1] https://lore.kernel.org/lkml/20231019132545.1190490-1-john.ogness@linutronix.de [2] https://lore.kernel.org/lkml/ZTkxOJbDLPy12n41@alley [3] https://lore.kernel.org/lkml/ZS-r3QnpKzm7UVip@alley John Ogness (8): printk: ringbuffer: Do not skip non-finalized records with prb_next_seq() printk: ringbuffer: Clarify special lpos values printk: For @suppress_panic_printk check for other CPU in panic printk: Add this_cpu_in_panic() printk: ringbuffer: Cleanup reader terminology printk: Wait for all reserved records with pr_flush() printk: Skip non-finalized records in panic printk: Avoid non-panic CPUs flooding ringbuffer Petr Mladek (1): printk: Disable passing console lock owner completely during panic() kernel/printk/internal.h | 1 + kernel/printk/printk.c | 108 ++++++---- kernel/printk/printk_ringbuffer.c | 343 +++++++++++++++++++++++++----- kernel/printk/printk_ringbuffer.h | 21 +- 4 files changed, 382 insertions(+), 91 deletions(-) base-commit: b4908d68609b57ad1ba4b80bd72c4d2260387e31 -- 2.39.2