From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932640AbaDWU4w (ORCPT ); Wed, 23 Apr 2014 16:56:52 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:59351 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1422655AbaDWU4I (ORCPT ); Wed, 23 Apr 2014 16:56:08 -0400 Date: Wed, 23 Apr 2014 13:56:06 -0700 From: Andrew Morton To: Jan Kara Cc: LKML , pmladek@suse.cz, Frederic Weisbecker , Steven Rostedt Subject: Re: [PATCH 2/8] printk: Release lockbuf_lock before calling console_trylock_for_printk() Message-Id: <20140423135606.d727fe5eb38bd8805ad3a5c3@linux-foundation.org> In-Reply-To: <1395770101-24534-3-git-send-email-jack@suse.cz> References: <1395770101-24534-1-git-send-email-jack@suse.cz> <1395770101-24534-3-git-send-email-jack@suse.cz> X-Mailer: Sylpheed 3.2.0beta5 (GTK+ 2.24.10; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 25 Mar 2014 18:54:55 +0100 Jan Kara wrote: > There's no reason to hold lockbuf_lock when entering > console_trylock_for_printk(). The first thing this function does is > calling down_trylock(console_sem) and if that fails it immediately > unlocks lockbuf_lock. So lockbuf_lock isn't needed for that branch. > When down_trylock() succeeds, the rest of console_trylock() is OK > without lockbuf_lock (it is called without it from other places), and > the only remaining thing in console_trylock_for_printk() is > can_use_console() call. For that call console_sem is enough (it > iterates all consoles and checks CON_ANYTIME flag). > > So we drop logbuf_lock before entering console_trylock_for_printk() > which simplifies the code. > I suppose we should document have_callable_console()'s locking requirements, and I don't think that "early in boot" part is true? --- a/kernel/printk/printk.c~printk-release-lockbuf_lock-before-calling-console_trylock_for_printk-fix +++ a/kernel/printk/printk.c @@ -1377,7 +1377,9 @@ static void zap_locks(void) sema_init(&console_sem, 1); } -/* Check if we have any console registered that can be called early in boot. */ +/* + * Check if we have any console registered. Requires console_sem. + */ static int have_callable_console(void) { struct console *con; _