From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933933Ab0FFBfe (ORCPT ); Sat, 5 Jun 2010 21:35:34 -0400 Received: from h5.dl5rb.org.uk ([81.2.74.5]:40454 "EHLO h5.dl5rb.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933768Ab0FFBfd (ORCPT ); Sat, 5 Jun 2010 21:35:33 -0400 Date: Sun, 6 Jun 2010 02:35:05 +0100 From: Ralf Baechle To: Andrew Morton Cc: Kevin Cernekee , mingo@elte.hu, simon.kagstrom@netinsight.net, David.Woodhouse@intel.com, lethal@linux-sh.org, linux-kernel@vger.kernel.org, linux-mips@linux-mips.org Subject: [PATCH v4] printk: fix delayed messages from CPU hotplug events Message-ID: <20100606013505.GB6169@linux-mips.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.20 (2009-08-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Kevin Cernekee printk: fix delayed messages from CPU hotplug events When a secondary CPU is being brought up, it is not uncommon for printk() to be invoked when cpu_online(smp_processor_id()) == 0. The case that I witnessed personally was on MIPS: http://lkml.org/lkml/2010/5/30/4 If (can_use_console() == 0), printk() will spool its output to log_buf and it will be visible in "dmesg", but that output will NOT be echoed to the console until somebody calls release_console_sem() from a CPU that is online. Therefore, the boot time messages from the new CPU can get stuck in "limbo" for a long time, and might suddenly appear on the screen when a completely unrelated event (e.g. "eth0: link is down") occurs. This patch modifies the console code so that any pending messages are automatically flushed out to the console whenever a CPU hotplug operation completes successfully or aborts. The issue was seen on 2.6.34. [Ralf: Cleanup patch posted by akpm merged into the patch] Signed-off-by: Kevin Cernekee To: To: To: To: To: Cc: Cc: Patchwork: http://patchwork.linux-mips.org/patch/1355/ Reviewed-by: Paul Mundt Patchwork: http://patchwork.linux-mips.org/patch/1356/ Signed-off-by: Ralf Baechle kernel/printk.c | 30 ++++++++++++++++++++++++++++-- 1 file changed, 28 insertions(+), 2 deletions(-) Index: linux-queue/kernel/printk.c =================================================================== --- linux-queue.orig/kernel/printk.c +++ linux-queue/kernel/printk.c @@ -37,6 +37,8 @@ #include #include #include +#include +#include #include @@ -985,6 +987,29 @@ void resume_console(void) } /** + * console_cpu_notify - print deferred console messages after CPU hotplug + * @self: notifier struct + * @action: CPU hotplug event + * @hcpu: unused + * + * If printk() is called from a CPU that is not online yet, the messages + * will be spooled but will not show up on the console. This function is + * called when a new CPU comes online (or fails to come up), and ensures + * that any such output gets printed. + */ +static int __cpuinit console_cpu_notify(struct notifier_block *self, + unsigned long action, void *hcpu) +{ + switch (action) { + case CPU_ONLINE: + case CPU_UP_CANCELED: + acquire_console_sem(); + release_console_sem(); + } + return NOTIFY_OK; +} + +/** * acquire_console_sem - lock the console system for exclusive use. * * Acquires a semaphore which guarantees that the caller has @@ -1371,7 +1396,7 @@ int unregister_console(struct console *c } EXPORT_SYMBOL(unregister_console); -static int __init disable_boot_consoles(void) +static int __init printk_late_init(void) { struct console *con; @@ -1382,9 +1407,10 @@ static int __init disable_boot_consoles( unregister_console(con); } } + hotcpu_notifier(console_cpu_notify, 0); return 0; } -late_initcall(disable_boot_consoles); +late_initcall(printk_late_init); #if defined CONFIG_PRINTK