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 X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 139F9C2BA19 for ; Thu, 9 Apr 2020 19:42:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DD6CC2084D for ; Thu, 9 Apr 2020 19:42:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726909AbgDITmu (ORCPT ); Thu, 9 Apr 2020 15:42:50 -0400 Received: from peace.netnation.com ([204.174.223.2]:46842 "EHLO peace.netnation.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726687AbgDITmt (ORCPT ); Thu, 9 Apr 2020 15:42:49 -0400 X-Greylist: delayed 1023 seconds by postgrey-1.27 at vger.kernel.org; Thu, 09 Apr 2020 15:42:49 EDT Received: from sim by peace.netnation.com with local (Exim 4.92) (envelope-from ) id 1jMco4-0008Me-5I; Thu, 09 Apr 2020 12:25:44 -0700 Date: Thu, 9 Apr 2020 12:25:44 -0700 From: Simon Kirby To: Sergey Senozhatsky , Greg Kroah-Hartman Cc: Petr Mladek , Sergey Senozhatsky , Steven Rostedt , linux-kernel@vger.kernel.org, Lech Perczak , Theodore Ts'o , John Ogness , Jann Horn Subject: Re: [PATCHv2] printk: queue wake_up_klogd irq_work only if per-CPU areas are ready Message-ID: <20200409192543.GA30816@hostway.ca> References: <20200303113002.63089-1-sergey.senozhatsky@gmail.com> <20200304152159.2p7d7dnztf433i24@pathway.suse.cz> <20200305013014.GA174444@google.com> <20200305185348.GB2141048@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200305185348.GB2141048@kroah.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 05, 2020 at 07:53:48PM +0100, Greg Kroah-Hartman wrote: > On Thu, Mar 05, 2020 at 10:30:14AM +0900, Sergey Senozhatsky wrote: > > On (20/03/04 16:21), Petr Mladek wrote: > > [..] > > > > Fix printk_deferred() and do not queue per-CPU irq_work > > > > before per-CPU areas are initialized. > > > > > > > > [0] https://lore.kernel.org/lkml/aa0732c6-5c4e-8a8b-a1c1-75ebe3dca05b@camlintechnologies.com/ > > > > > > > > Signed-off-by: Sergey Senozhatsky > > > > Reported-by: Lech Perczak > > > > Cc: Greg Kroah-Hartman > > > > Cc: Theodore Ts'o > > > > Cc: John Ogness > > > > > > Reviewed-by: Petr Mladek > > > > Thanks! > > > > > Now, the question is whether to hurry this fix into 5.6 or if > > > it could wait for 5.7. > > > > > > I think that it could wait because 5.6 is not affected by > > > the particular printk_deferred(). This patch fixes a long-term > > > generic problem. But I am open for other opinions. > > > > Good question. My 5 cents, I would _probably_ push it now. Not > > because it fixes any known issues on 5.6, but because we have > > a number of LTS kernel (4.19, 4.14, 4.9, 4.4, 3.16) that can be > > affected should 1b710b1b10eff9d4 be backported to those kernels. > > It was backported there, and now has been reverted. So no big rush from > what I can tell. This causes "dmesg -w" or "cat /dev/kmsg" to not print new messages after dumping the current ring. I hit this on v5.5.9, v5.5.15, v5.6.3, and Linus HEAD. This prints no "hi": (sleep 1;echo hi > /dev/kmsg)& dmesg -w ...curiously, "strace dmesg -w" shows the data received once ^C is hit. Jann pointed me to this patch. Applying it or reverting 1b710b1b10eff9d4 does fix it for me. However, Linus HEAD is still broken and, AFAICS, remains unreverted and unfixed in stable/linux-5.4.y through linux-5.6.y. It was introduced in 5.6 but backported to those, not just the LTS above. Simon-