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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 9078BC43215 for ; Sat, 16 Nov 2019 16:28:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 68337214DE for ; Sat, 16 Nov 2019 16:28:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573921696; bh=a3atx0pDJ6BtMgQLn3IDaJgOpT1UTvSQakhdCHeRKyI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=EG1njNrOG/k0NRU3zRZDbWx+5F12OglzfDlEHtTzbsq8cuZkiJn6IuWLgMcZ7l528 N+fjOExQuYEA9u9QA/LiveaXp3Pwm79wo4Kzg99Zt50zYmaFrcX6gjV8hJSZ2inhuh zlu2um+t1l7aFbTV9U4CJ4vwtElG/7bibep9YI9E= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727835AbfKPPlU (ORCPT ); Sat, 16 Nov 2019 10:41:20 -0500 Received: from mail.kernel.org ([198.145.29.99]:44208 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727763AbfKPPlQ (ORCPT ); Sat, 16 Nov 2019 10:41:16 -0500 Received: from sasha-vm.mshome.net (unknown [50.234.116.4]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 493F220733; Sat, 16 Nov 2019 15:41:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573918875; bh=a3atx0pDJ6BtMgQLn3IDaJgOpT1UTvSQakhdCHeRKyI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=LNqG2zevJiQaJAVKOa2Ta9dY9h6Pu04D8qyjXO6i/TW/xT/JF5KTFM0IkGPzDC3cQ UNKlUXFM9LVtTEeYJtBGZ6JbiiorwMu3v1/UKP19p5SnuqjSUo0UuDSAsQyN4PMbyq j704dUngPPQVf+mC8l42kU58ILxJkUilN4TWBZRw= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Sergey Senozhatsky , Andrew Morton , Dmitriy Vyukov , Tetsuo Handa , Tejun Heo , Peter Zijlstra , Sergey Senozhatsky , Petr Mladek , Sasha Levin Subject: [PATCH AUTOSEL 4.19 003/237] printk: lock/unlock console only for new logbuf entries Date: Sat, 16 Nov 2019 10:37:18 -0500 Message-Id: <20191116154113.7417-3-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20191116154113.7417-1-sashal@kernel.org> References: <20191116154113.7417-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Sergey Senozhatsky [ Upstream commit 3ac37a93fa9217e576bebfd4ba3e80edaaeb2289 ] Prior to commit 5c2992ee7fd8a29 ("printk: remove console flushing special cases for partial buffered lines") we would do console_cont_flush() for each pr_cont() to print cont fragments, so console_unlock() would actually print data: pr_cont(); console_lock(); console_unlock() console_cont_flush(); // print cont fragment ... pr_cont(); console_lock(); console_unlock() console_cont_flush(); // print cont fragment We don't do console_cont_flush() anymore, so when we do pr_cont() console_unlock() does nothing (unless we flushed the cont buffer): pr_cont(); console_lock(); console_unlock(); // noop ... pr_cont(); console_lock(); console_unlock(); // noop ... pr_cont(); cont_flush(); console_lock(); console_unlock(); // print data We also wakeup klogd purposelessly for pr_cont() output - un-flushed cont buffer is not stored in log_buf; there is nothing to pull. Thus we can console_lock()/console_unlock()/wake_up_klogd() only when we know that we log_store()-ed a message and there is something to print to the consoles/syslog. Link: http://lkml.kernel.org/r/20181002023836.4487-3-sergey.senozhatsky@gmail.com To: Steven Rostedt Cc: Andrew Morton Cc: Dmitriy Vyukov Cc: Tetsuo Handa Cc: Tejun Heo Cc: Peter Zijlstra Cc: LKML Cc: Sergey Senozhatsky Signed-off-by: Sergey Senozhatsky Signed-off-by: Petr Mladek Signed-off-by: Sasha Levin --- kernel/printk/printk.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index d0d03223b45b1..9ee6016a19fc8 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1894,8 +1894,9 @@ asmlinkage int vprintk_emit(int facility, int level, const char *fmt, va_list args) { int printed_len; - bool in_sched = false; + bool in_sched = false, pending_output; unsigned long flags; + u64 curr_log_seq; if (level == LOGLEVEL_SCHED) { level = LOGLEVEL_DEFAULT; @@ -1907,11 +1908,13 @@ asmlinkage int vprintk_emit(int facility, int level, /* This stops the holder of console_sem just where we want him */ logbuf_lock_irqsave(flags); + curr_log_seq = log_next_seq; printed_len = vprintk_store(facility, level, dict, dictlen, fmt, args); + pending_output = (curr_log_seq != log_next_seq); logbuf_unlock_irqrestore(flags); /* If called from the scheduler, we can not call up(). */ - if (!in_sched) { + if (!in_sched && pending_output) { /* * Disable preemption to avoid being preempted while holding * console_sem which would prevent anyone from printing to @@ -1928,7 +1931,8 @@ asmlinkage int vprintk_emit(int facility, int level, preempt_enable(); } - wake_up_klogd(); + if (pending_output) + wake_up_klogd(); return printed_len; } EXPORT_SYMBOL(vprintk_emit); -- 2.20.1