* Ingo Molnar <mingo@xxxxxxx> wrote: > If the ticks stop this suggests a lockup within the printk code. > [...] In which case the printk-killswitch patch below (to be applied *instead* of the previous debugging patch i sent) should provide the desired NMI watchdog output on the serial console. Warning: it's entirely untested. Thanks, Ingo arch/x86/kernel/early_printk.c | 2 +- include/linux/printk.h | 4 ++++ kernel/printk.c | 18 ++++++++++++++++++ kernel/watchdog.c | 7 +++++++ 4 files changed, 30 insertions(+), 1 deletions(-) diff --git a/arch/x86/kernel/early_printk.c b/arch/x86/kernel/early_printk.c index cd28a35..d75fd66 100644 --- a/arch/x86/kernel/early_printk.c +++ b/arch/x86/kernel/early_printk.c @@ -171,7 +171,7 @@ static struct console early_serial_console = { /* Direct interface for emergencies */ static struct console *early_console = &early_vga_console; -static int __initdata early_console_initialized; +int early_console_initialized; asmlinkage void early_printk(const char *fmt, ...) { diff --git a/include/linux/printk.h b/include/linux/printk.h index 0101d55..7393291 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -88,6 +88,8 @@ int no_printk(const char *fmt, ...) return 0; } +extern int early_console_initialized; + extern asmlinkage __attribute__ ((format (printf, 1, 2))) void early_printk(const char *fmt, ...); @@ -114,6 +116,8 @@ extern int printk_delay_msec; extern int dmesg_restrict; extern int kptr_restrict; +extern void printk_kill(void); + void log_buf_kexec_setup(void); void __init setup_log_buf(int early); #else diff --git a/kernel/printk.c b/kernel/printk.c index 3518539..f6193e1 100644 --- a/kernel/printk.c +++ b/kernel/printk.c @@ -519,6 +519,19 @@ static void __call_console_drivers(unsigned start, unsigned end) } } +/* + * 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 int __read_mostly printk_killswitch; + +void printk_kill(void) +{ + printk_killswitch = 1; +} + static int __read_mostly ignore_loglevel; static int __init ignore_loglevel_setup(char *str) @@ -833,6 +846,10 @@ asmlinkage int vprintk(const char *fmt, va_list args) size_t plen; char special; + /* Return early if a debugging subsystem has killed printk output: */ + if (unlikely(printk_killswitch)) + return 1; + boot_delay_msec(); printk_delay(); @@ -1533,6 +1550,7 @@ void register_console(struct console *newcon) for_each_console(bcon) if (bcon->flags & CON_BOOT) unregister_console(bcon); + early_console_initialized = 0; } else { printk(KERN_INFO "%sconsole [%s%d] enabled\n", (newcon->flags & CON_BOOT) ? "boot" : "" , diff --git a/kernel/watchdog.c b/kernel/watchdog.c index 3d0c56a..6e9b109 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -234,6 +234,13 @@ static void watchdog_overflow_callback(struct perf_event *event, int nmi, 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: + */ + if (early_console_initialized) + printk_kill(); + if (hardlockup_panic) panic("Watchdog detected hard LOCKUP on cpu %d", this_cpu); else -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html