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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 9FD77C43381 for ; Mon, 4 Mar 2019 07:39:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6DE78206B8 for ; Mon, 4 Mar 2019 07:39:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="sg+XsU1e" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726197AbfCDHjC (ORCPT ); Mon, 4 Mar 2019 02:39:02 -0500 Received: from mail-pg1-f195.google.com ([209.85.215.195]:43770 "EHLO mail-pg1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725550AbfCDHjB (ORCPT ); Mon, 4 Mar 2019 02:39:01 -0500 Received: by mail-pg1-f195.google.com with SMTP id l11so2451985pgq.10; Sun, 03 Mar 2019 23:39:01 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=ImeATGrc/HA5GiNT/68WVUj+Vhz5vM8oxHAmuWTiKWE=; b=sg+XsU1e0BP/Rdj+C5onxPQm93nzcRrL8r1AxSExaoXMosx8IMQEe7uGk6BqwDX4AV 8HLVyhW3hc44uBz7XpVut8lb0kxLW4dZyWHNdMZ5mE591DhMBYgaBCdtf0pCdYXoWVhf 0T/r4bY9nNvCvVf0ZFR1XwzUVDxmUNWQkvCbYoSlWb5aRulimH9WZlYE1OX9sstl//Lj JPlDjtxDC57edOfikj9mrwq+3gDHNRO0rnWF/IqydFwwLTSXOPc8TER99mCanxNeJkTs N4nj86jUgrRZ4cYL0UmU2cBZfq3asCemhqoSpya9/mDJ74xeUCB6yLcEOMpGs1h6O4ag LkhA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=ImeATGrc/HA5GiNT/68WVUj+Vhz5vM8oxHAmuWTiKWE=; b=ibxFk5Xla/3boS2n4QElbQCLMeCyYm6pGRvT1ntKQXUUIki0Bjk2gkG+nVuqRFv41X N5C0pgablvwP4cuTRZr/CsSDcsJpsCrj9xk1bfZ4krtmuSJ+w0DbqaEDozLKrBVkDJaq lt17HgZ4Dsf5B1RvevrcW6hse/ARQfJOCQM4w6jBlDtIzLKPnVxu4jemJl8Mw2dEVKp6 rnNZmoKJE1B39LiZZq+DFeYld04v9dROh1RY3hzZOeJZPkp1jAnK5hlW47jqolC8aExg V71m0ffQX5dAXhs9onHZSxUVhr8NMaZ+p6G+kfA+gozcLtXCblaRBaClyRObOvz0k40p a2GQ== X-Gm-Message-State: APjAAAX0tUvD8Cgqx3CK2QeK6Qmlg7+3x7G2Mi4h+uzNeulR4KAcgoNs JWAHwAFesbKJPxTn7w/sXG898nEw X-Google-Smtp-Source: APXvYqyYuglzqWWG0gwB5LHo9qWpvLsUKRtpwx6aNJEaOMmDKQa8iwXiz2IWtZVd1v0RgTzAiAasKw== X-Received: by 2002:a65:4384:: with SMTP id m4mr17161079pgp.375.1551685140931; Sun, 03 Mar 2019 23:39:00 -0800 (PST) Received: from localhost ([175.223.38.45]) by smtp.gmail.com with ESMTPSA id t4sm2953574pfh.117.2019.03.03.23.38.59 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sun, 03 Mar 2019 23:38:59 -0800 (PST) Date: Mon, 4 Mar 2019 16:38:56 +0900 From: Sergey Senozhatsky To: John Ogness Cc: linux-kernel@vger.kernel.org, Peter Zijlstra , Petr Mladek , Sergey Senozhatsky , Steven Rostedt , Daniel Wang , Andrew Morton , Linus Torvalds , Greg Kroah-Hartman , Alan Cox , Jiri Slaby , Peter Feiner , linux-serial@vger.kernel.org, Sergey Senozhatsky Subject: Re: [RFC PATCH v1 08/25] printk: add ring buffer and kthread Message-ID: <20190304073856.GA552@jagdpanzerIV> References: <20190212143003.48446-1-john.ogness@linutronix.de> <20190212143003.48446-9-john.ogness@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190212143003.48446-9-john.ogness@linutronix.de> User-Agent: Mutt/1.11.3 (2019-02-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (02/12/19 15:29), John Ogness wrote: [..] > + /* the printk kthread never exits */ > + for (;;) { > + ret = prb_iter_wait_next(&iter, buf, > + PRINTK_RECORD_MAX, &master_seq); > + if (ret == -ERESTARTSYS) { > + continue; > + } else if (ret < 0) { > + /* iterator invalid, start over */ > + prb_iter_init(&iter, &printk_rb, NULL); > + continue; > + } > + > + msg = (struct printk_log *)buf; > + format_text(msg, master_seq, ext_text, &ext_len, text, > + &len, printk_time); > + > + console_lock(); > + if (len > 0 || ext_len > 0) { > + call_console_drivers(ext_text, ext_len, text, len); > + boot_delay_msec(msg->level); > + printk_delay(); > + } > + console_unlock(); > + } This, theoretically, creates a whole new world of possibilities for console drivers. Now they can do GFP_KERNEL allocations and stall printk_kthread during OOM; or they can explicitly reschedule from ->write() callback (via console_conditional_schedule()) because console_lock() sets console_may_schedule. It's one thing to do cond_resched() (or to let preemption to take over) after call_console_drivers() (when we are done printing a message to all console drivers) and another thing to let preemption to take over while we are printing a messages to the consoles. It probably would make sense to disable preemption around call_console_drivers(). -ss