From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756224AbaCYRzW (ORCPT ); Tue, 25 Mar 2014 13:55:22 -0400 Received: from cantor2.suse.de ([195.135.220.15]:58438 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755870AbaCYRzP (ORCPT ); Tue, 25 Mar 2014 13:55:15 -0400 From: Jan Kara To: Andrew Morton Cc: LKML , pmladek@suse.cz, Frederic Weisbecker , Steven Rostedt , Jan Kara Subject: [PATCH 2/8] printk: Release lockbuf_lock before calling console_trylock_for_printk() Date: Tue, 25 Mar 2014 18:54:55 +0100 Message-Id: <1395770101-24534-3-git-send-email-jack@suse.cz> X-Mailer: git-send-email 1.8.1.4 In-Reply-To: <1395770101-24534-1-git-send-email-jack@suse.cz> References: <1395770101-24534-1-git-send-email-jack@suse.cz> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Signed-off-by: Jan Kara --- kernel/printk/printk.c | 49 +++++++++++++++++-------------------------------- 1 file changed, 17 insertions(+), 32 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index bd7ee2a9f960..7a8ffd89875c 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -249,9 +249,6 @@ static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN); static char *log_buf = __log_buf; static u32 log_buf_len = __LOG_BUF_LEN; -/* cpu currently holding logbuf_lock */ -static volatile unsigned int logbuf_cpu = UINT_MAX; - /* human readable text of the record */ static char *log_text(const struct printk_log *msg) { @@ -1332,36 +1329,22 @@ static inline int can_use_console(unsigned int cpu) * messages from a 'printk'. Return true (and with the * console_lock held, and 'console_locked' set) if it * is successful, false otherwise. - * - * This gets called with the 'logbuf_lock' spinlock held and - * interrupts disabled. It should return with 'lockbuf_lock' - * released but interrupts still disabled. */ static int console_trylock_for_printk(unsigned int cpu) - __releases(&logbuf_lock) { - int retval = 0, wake = 0; - - if (console_trylock()) { - retval = 1; - - /* - * If we can't use the console, we need to release - * the console semaphore by hand to avoid flushing - * the buffer. We need to hold the console semaphore - * in order to do this test safely. - */ - if (!can_use_console(cpu)) { - console_locked = 0; - wake = 1; - retval = 0; - } - } - logbuf_cpu = UINT_MAX; - raw_spin_unlock(&logbuf_lock); - if (wake) + if (!console_trylock()) + return 0; + /* + * If we can't use the console, we need to release the console + * semaphore by hand to avoid flushing the buffer. We need to hold the + * console semaphore in order to do this test safely. + */ + if (!can_use_console(cpu)) { + console_locked = 0; up(&console_sem); - return retval; + return 0; + } + return 1; } int printk_delay_msec __read_mostly; @@ -1494,6 +1477,9 @@ asmlinkage int vprintk_emit(int facility, int level, unsigned long flags; int this_cpu; int printed_len = 0; + /* cpu currently holding logbuf_lock in this function */ + static volatile unsigned int logbuf_cpu = UINT_MAX; + boot_delay_msec(level); printk_delay(); @@ -1609,13 +1595,12 @@ asmlinkage int vprintk_emit(int facility, int level, } printed_len += text_len; + logbuf_cpu = UINT_MAX; + raw_spin_unlock(&logbuf_lock); /* * Try to acquire and then immediately release the console semaphore. * The release will print out buffers and wake up /dev/kmsg and syslog() * users. - * - * The console_trylock_for_printk() function will release 'logbuf_lock' - * regardless of whether it actually gets the console semaphore or not. */ if (console_trylock_for_printk(this_cpu)) console_unlock(); -- 1.8.1.4