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=-5.4 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 9501DC2D0E2 for ; Thu, 24 Sep 2020 13:06:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4175E235FD for ; Thu, 24 Sep 2020 13:06:29 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="JnQ+jMZI" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727895AbgIXNG2 (ORCPT ); Thu, 24 Sep 2020 09:06:28 -0400 Received: from mx2.suse.de ([195.135.220.15]:33544 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727704AbgIXNG1 (ORCPT ); Thu, 24 Sep 2020 09:06:27 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1600952786; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=vWhiMTbLKygzkeBmeWC4lp5Kk4n1lEhbQG0ng2LQOwg=; b=JnQ+jMZI1Zc6Y4y3PEceyIqKyNVXM2TxZpCDIbLQRE/Po5zKgakoC4xUenVAufJ1yItiSA HAR4J/iP6F1eBhn/Mt6YLcJ8dDMUhYXORd6P+Vq3SsOpHbQQsWtn6IpYMJ/DuaS/Fko9Rv r7D1qzVRqbjoj8wfniprG6vHMKGUx84= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 4AE7EAF2C; Thu, 24 Sep 2020 13:06:26 +0000 (UTC) Date: Thu, 24 Sep 2020 15:06:25 +0200 From: Petr Mladek To: Sergey Senozhatsky Cc: Steven Rostedt , John Ogness , Linus Torvalds , Thomas Gleixner , Prarit Bhargava , Mark Salyzyn , Chunyan Zhang , Orson Zhai , Changki Kim , Sergey Senozhatsky , linux-kernel@vger.kernel.org Subject: Re: [RFC 2/2] printk: Add more information about the printk caller Message-ID: <20200924130625.GD29288@alley> References: <20200923135617.27149-1-pmladek@suse.com> <20200923135617.27149-3-pmladek@suse.com> <20200924021756.GD577@jagdpanzerIV.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200924021756.GD577@jagdpanzerIV.localdomain> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 2020-09-24 11:17:56, Sergey Senozhatsky wrote: > On (20/09/23 15:56), Petr Mladek wrote: > [..] > > /* > > * To reduce unnecessarily reopening, first check if the descriptor > > - * state and caller ID are correct. > > + * state and caller infromation are correct. > > */ > > - d_state = desc_read(desc_ring, id, &desc, NULL, &cid); > > - if (d_state != desc_committed || cid != caller_id) > > + d_state = desc_read(desc_ring, id, &desc, NULL, &cal); > > + if (d_state != desc_committed || > > + cal.pid != caller->pid || > > + cal.cpu_ctx != caller->cpu_ctx) { > > You probably might want to factor out ctx check into a static > inline helper. Since you use this check in several places, and > we may check more context fields in the future. Makes sense. > [..] > > +/* Information about the process and context that adds the message */ > > +struct printk_caller { > > + pid_t pid; /* thread id */ > > + u32 cpu_ctx; /* processor id and interrupt context */ > > +}; > > A question. Suppose we have a task which does > > CPU0 > > pr_err(...); > > preempt_disable(); > pr_err(...); > preempt_enable(); > > pr_err(...); > > rcu_read_lock(); > pr_info(...); > rcu_read_unlock(); > > Should we distinguish those as 3 different contexts? > > - normal printk > - printk under disabled preemption (affects scheduling) > - printk under RCU read side lock (affects RCU grace periods) Good question. Well, these contexts could not get detected in PREEMPT_NONE or PREEMPT_VOLUNTARY. Also I wonder where it would stop. There are several RCU flavors. I would not distinguish them unless there is a real demand. Best Regards, Petr