Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751169Ab2KPCWF (ORCPT ); Thu, 15 Nov 2012 21:22:05 -0500 Received: from mail-vc0-f174.google.com ([209.85.220.174]:61094 "EHLO mail-vc0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751608Ab2KPCWA (ORCPT ); Thu, 15 Nov 2012 21:22:00 -0500 From: Frederic Weisbecker To: LKML Cc: Frederic Weisbecker , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Andrew Morton , Steven Rostedt , Paul Gortmaker Subject: [PATCH 9/9] printk: Wake up klogd using irq_work Date: Fri, 16 Nov 2012 03:21:31 +0100 Message-Id: <1353032491-16462-10-git-send-email-fweisbec@gmail.com> X-Mailer: git-send-email 1.7.5.4 In-Reply-To: <1353032491-16462-1-git-send-email-fweisbec@gmail.com> References: <1353032491-16462-1-git-send-email-fweisbec@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4919 Lines: 154 klogd is woken up asynchronously from the tick in order to do it safely. However if printk is called when the tick is stopped, the reader won't be woken up until the next interrupt, which might not fire for a while. As a result, the user may miss some message. To fix this, lets implement the printk tick using a lazy irq work. This subsystem takes care of the timer tick state and can fix up accordingly. Signed-off-by: Frederic Weisbecker Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Andrew Morton Cc: Steven Rostedt Cc: Paul Gortmaker --- include/linux/printk.h | 3 --- init/Kconfig | 1 + kernel/printk.c | 36 ++++++++++++++++++++---------------- kernel/time/tick-sched.c | 2 +- kernel/timer.c | 1 - 5 files changed, 22 insertions(+), 21 deletions(-) diff --git a/include/linux/printk.h b/include/linux/printk.h index 9afc01e..86c4b62 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -98,9 +98,6 @@ int no_printk(const char *fmt, ...) extern asmlinkage __printf(1, 2) void early_printk(const char *fmt, ...); -extern int printk_needs_cpu(int cpu); -extern void printk_tick(void); - #ifdef CONFIG_PRINTK asmlinkage __printf(5, 0) int vprintk_emit(int facility, int level, diff --git a/init/Kconfig b/init/Kconfig index cdc152c..c575566 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1196,6 +1196,7 @@ config HOTPLUG config PRINTK default y bool "Enable support for printk" if EXPERT + select IRQ_WORK help This option enables normal printk support. Removing it eliminates most of the message strings from the kernel image diff --git a/kernel/printk.c b/kernel/printk.c index 2d607f4..c9104fe 100644 --- a/kernel/printk.c +++ b/kernel/printk.c @@ -42,6 +42,7 @@ #include #include #include +#include #include @@ -1955,30 +1956,32 @@ int is_console_locked(void) static DEFINE_PER_CPU(int, printk_pending); static DEFINE_PER_CPU(char [PRINTK_BUF_SIZE], printk_sched_buf); -void printk_tick(void) +static void wake_up_klogd_work_func(struct irq_work *irq_work) { - if (__this_cpu_read(printk_pending)) { - int pending = __this_cpu_xchg(printk_pending, 0); - if (pending & PRINTK_PENDING_SCHED) { - char *buf = __get_cpu_var(printk_sched_buf); - printk(KERN_WARNING "[sched_delayed] %s", buf); - } - if (pending & PRINTK_PENDING_WAKEUP) - wake_up_interruptible(&log_wait); + int pending = __this_cpu_xchg(printk_pending, 0); + + if (pending & PRINTK_PENDING_SCHED) { + char *buf = __get_cpu_var(printk_sched_buf); + printk(KERN_WARNING "[sched_delayed] %s", buf); } -} -int printk_needs_cpu(int cpu) -{ - if (cpu_is_offline(cpu)) - printk_tick(); - return __this_cpu_read(printk_pending); + if (pending & PRINTK_PENDING_WAKEUP) + wake_up_interruptible(&log_wait); } +static DEFINE_PER_CPU(struct irq_work, wake_up_klogd_work) = { + .func = wake_up_klogd_work_func, + .flags = IRQ_WORK_LAZY, +}; + void wake_up_klogd(void) { - if (waitqueue_active(&log_wait)) + preempt_disable(); + if (waitqueue_active(&log_wait)) { this_cpu_or(printk_pending, PRINTK_PENDING_WAKEUP); + irq_work_queue(&__get_cpu_var(wake_up_klogd_work)); + } + preempt_enable(); } static void console_cont_flush(char *text, size_t size) @@ -2458,6 +2461,7 @@ int printk_sched(const char *fmt, ...) va_end(args); __this_cpu_or(printk_pending, PRINTK_PENDING_SCHED); + irq_work_queue(&__get_cpu_var(wake_up_klogd_work)); local_irq_restore(flags); return r; diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index f249e8c..822d757 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -289,7 +289,7 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts, time_delta = timekeeping_max_deferment(); } while (read_seqretry(&xtime_lock, seq)); - if (rcu_needs_cpu(cpu, &rcu_delta_jiffies) || printk_needs_cpu(cpu) || + if (rcu_needs_cpu(cpu, &rcu_delta_jiffies) || arch_needs_cpu(cpu) || irq_work_needs_cpu()) { next_jiffies = last_jiffies + 1; delta_jiffies = 1; diff --git a/kernel/timer.c b/kernel/timer.c index 367d008..ff3b516 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -1351,7 +1351,6 @@ void update_process_times(int user_tick) account_process_tick(p, user_tick); run_local_timers(); rcu_check_callbacks(cpu, user_tick); - printk_tick(); #ifdef CONFIG_IRQ_WORK if (in_irq()) irq_work_run(); -- 1.7.5.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/