From 1c6f7f178af39e484583a091c34a5a0b35f99c46 Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Fri, 22 Jul 2011 17:58:40 +0200 Subject: [PATCH 067/365] printk: Add a printk kill switch Add a prinkt-kill-switch. This is used from (NMI) watchdog to ensure that it does not dead-lock with the early printk code. Change-Id: Id189c263b6a1572e9967ee5a213f10ba2e634784 Signed-off-by: Thomas Gleixner --- include/linux/printk.h | 2 ++ kernel/printk/printk.c | 79 +++++++++++++++++++++++++++++++----------- kernel/watchdog_hld.c | 9 +++++ 3 files changed, 69 insertions(+), 21 deletions(-) diff --git a/include/linux/printk.h b/include/linux/printk.h index 45993a72ee43..c666419e8e6a 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -127,9 +127,11 @@ struct va_format { #ifdef CONFIG_EARLY_PRINTK extern asmlinkage __printf(1, 2) void early_printk(const char *fmt, ...); +extern void printk_kill(void); #else static inline __printf(1, 2) __cold void early_printk(const char *s, ...) { } +static inline void printk_kill(void) { } #endif #ifdef CONFIG_PRINTK_NMI diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 673aadadf6c4..5c62cfde8cf2 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -374,7 +374,6 @@ __packed __aligned(4) * console_unlock() or anything else that might wake up a process. */ DEFINE_RAW_SPINLOCK(logbuf_lock); - /* * Helper macros to lock/unlock logbuf_lock and switch between * printk-safe/unsafe modes. @@ -402,6 +401,57 @@ DEFINE_RAW_SPINLOCK(logbuf_lock); raw_spin_unlock(&logbuf_lock); \ printk_safe_exit_irqrestore(flags); \ } while (0) +#ifdef CONFIG_EARLY_PRINTK +struct console *early_console; + +static void early_vprintk(const char *fmt, va_list ap) +{ + if (early_console) { + char buf[512]; + int n = vscnprintf(buf, sizeof(buf), fmt, ap); + + early_console->write(early_console, buf, n); + } +} + +asmlinkage void early_printk(const char *fmt, ...) +{ + va_list ap; + + va_start(ap, fmt); + early_vprintk(fmt, ap); + va_end(ap); +} + +/* + * This is independent of any log levels - a global + * kill switch that turns off all of printk. + * + * Used by the NMI watchdog if early-printk is enabled. + */ +static bool __read_mostly printk_killswitch; + +void printk_kill(void) +{ + printk_killswitch = true; +} + +#ifdef CONFIG_PRINTK +static int forced_early_printk(const char *fmt, va_list ap) +{ + if (!printk_killswitch) + return 0; + early_vprintk(fmt, ap); + return 1; +} +#endif + +#else +static inline int forced_early_printk(const char *fmt, va_list ap) +{ + return 0; +} +#endif #ifdef CONFIG_PRINTK DECLARE_WAIT_QUEUE_HEAD(log_wait); @@ -1770,6 +1820,13 @@ asmlinkage int vprintk_emit(int facility, int level, int printed_len = 0; bool in_sched = false; + /* + * Fall back to early_printk if a debugging subsystem has + * killed printk output + */ + if (unlikely(forced_early_printk(fmt, args))) + return 1; + if (level == LOGLEVEL_SCHED) { level = LOGLEVEL_DEFAULT; in_sched = true; @@ -1952,26 +2009,6 @@ static bool suppress_message_printing(int level) { return false; } #endif /* CONFIG_PRINTK */ -#ifdef CONFIG_EARLY_PRINTK -struct console *early_console; - -asmlinkage __visible void early_printk(const char *fmt, ...) -{ - va_list ap; - char buf[512]; - int n; - - if (!early_console) - return; - - va_start(ap, fmt); - n = vscnprintf(buf, sizeof(buf), fmt, ap); - va_end(ap); - - early_console->write(early_console, buf, n); -} -#endif - static int __add_preferred_console(char *name, int idx, char *options, char *brl_options) { diff --git a/kernel/watchdog_hld.c b/kernel/watchdog_hld.c index e5709b8603ac..9566409a1d50 100644 --- a/kernel/watchdog_hld.c +++ b/kernel/watchdog_hld.c @@ -25,6 +25,7 @@ static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved); #ifdef CONFIG_HARDLOCKUP_DETECTOR_OTHER_CPU static cpumask_t __read_mostly watchdog_cpus; #endif +static DEFINE_RAW_SPINLOCK(watchdog_output_lock); /* boot commands */ /* @@ -240,6 +241,13 @@ static void watchdog_overflow_callback(struct perf_event *event, /* only print hardlockups once */ if (__this_cpu_read(hard_watchdog_warn) == true) return; + /* + * If early-printk is enabled then make sure we do not + * lock up in printk() and kill console logging: + */ + printk_kill(); + + raw_spin_lock(&watchdog_output_lock); pr_emerg("Watchdog detected hard LOCKUP on cpu %d", this_cpu); print_modules(); @@ -257,6 +265,7 @@ static void watchdog_overflow_callback(struct perf_event *event, !test_and_set_bit(0, &hardlockup_allcpu_dumped)) trigger_allbutself_cpu_backtrace(); + raw_spin_unlock(&watchdog_output_lock); if (hardlockup_panic) nmi_panic(regs, "Hard LOCKUP"); -- 2.28.0