From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756250Ab1FEOpV (ORCPT ); Sun, 5 Jun 2011 10:45:21 -0400 Received: from mo-p00-ob.rzone.de ([81.169.146.160]:10193 "EHLO mo-p00-ob.rzone.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753710Ab1FEOpS (ORCPT ); Sun, 5 Jun 2011 10:45:18 -0400 X-RZG-AUTH: :IGUXYVOIf/Z0yAghYbpIhzghmj8icP68r1arC3zTx2B9G7/X5zri/u5Y1+fsZ6BmRA== X-RZG-CLASS-ID: mo00 Message-ID: <4DEB9673.4000204@die-jansens.de> Date: Sun, 05 Jun 2011 16:45:07 +0200 From: Arne Jansen User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.17) Gecko/20110424 Thunderbird/3.1.10 MIME-Version: 1.0 To: Ingo Molnar CC: Peter Zijlstra , Linus Torvalds , mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org, efault@gmx.de, npiggin@kernel.dk, akpm@linux-foundation.org, frank.rowand@am.sony.com, tglx@linutronix.de, linux-tip-commits@vger.kernel.org Subject: Re: [debug patch] printk: Add a printk killswitch to robustify NMI watchdog messages References: <20110605081747.GA17920@elte.hu> <4DEB4FA7.3050400@die-jansens.de> <20110605095555.GA22058@elte.hu> <4DEB58D8.4000805@die-jansens.de> <20110605110132.GB23463@elte.hu> <20110605111933.GA24592@elte.hu> <20110605113627.GA25724@elte.hu> <4DEB6F3A.3000109@die-jansens.de> <20110605133958.GA27812@elte.hu> <4DEB8A93.30601@die-jansens.de> <20110605140602.GA29338@elte.hu> In-Reply-To: <20110605140602.GA29338@elte.hu> Content-Type: multipart/mixed; boundary="------------010400080107020202000007" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is a multi-part message in MIME format. --------------010400080107020202000007 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit On 05.06.2011 16:06, Ingo Molnar wrote: > > * Arne Jansen wrote: > >> On 05.06.2011 15:39, Ingo Molnar wrote: >>> >>> * Arne Jansen wrote: >>> >>>>>> Warning: it's entirely untested. >>>> >>>> How is the output supposed to come through? shouldn't printk revert >>>> to early_printk instead of just returning? >>> >>> oh, right you are. >>> >>> Does the patch below work? It does early-printk within printk(). >> >> Too late, I already built my on early_vprintk ;) > > heh :-) > > Mind posting the patch? Your tested patch is infinitely more valuable > than my not-even-build-tested patch ;-) It's basically just your patch. I attached it nevertheless... -Arne --------------010400080107020202000007 Content-Type: text/x-patch; name="printk_kill.patch" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="printk_kill.patch" diff --git a/arch/x86/kernel/early_printk.c b/arch/x86/kernel/early_printk.c index cd28a35..0623126 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, ...) { @@ -185,6 +185,15 @@ asmlinkage void early_printk(const char *fmt, ...) va_end(ap); } +asmlinkage void early_vprintk(const char *fmt, va_list ap) +{ + char buf[512]; + int n; + + n = vscnprintf(buf, sizeof(buf), fmt, ap); + early_console->write(early_console, buf, n); +} + static inline void early_console_register(struct console *con, int keep_early) { if (early_console->index != -1) { diff --git a/include/linux/printk.h b/include/linux/printk.h index ee048e7..6bb6963 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -86,8 +86,11 @@ 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, ...); +void early_vprintk(const char *fmt, va_list args); extern int printk_needs_cpu(int cpu); extern void printk_tick(void); @@ -112,6 +115,8 @@ extern int printk_delay_msec; extern int dmesg_restrict; extern int kptr_restrict; +extern void printk_kill(void); + void log_buf_kexec_setup(void); #else static inline __attribute__ ((format (printf, 1, 0))) diff --git a/kernel/printk.c b/kernel/printk.c index da8ca81..38f880f 100644 --- a/kernel/printk.c +++ b/kernel/printk.c @@ -490,6 +490,19 @@ 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) @@ -804,6 +817,15 @@ asmlinkage int vprintk(const char *fmt, va_list args) size_t plen; char special; + /* + * Fall back to early_printk if a debugging subsystem has + * killed printk output + */ + if (unlikely(printk_killswitch)) { + early_vprintk(fmt, args); + return 1; + } + boot_delay_msec(); printk_delay(); @@ -1504,6 +1526,7 @@ 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 140dce7..18fca3d 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -197,6 +197,8 @@ static struct perf_event_attr wd_hw_attr = { .disabled = 1, }; +static DEFINE_SPINLOCK(watchdog_output_lock); + /* Callback function for perf event subsystem */ static void watchdog_overflow_callback(struct perf_event *event, int nmi, struct perf_sample_data *data, @@ -223,10 +225,20 @@ static void watchdog_overflow_callback(struct perf_event *event, int nmi, if (__this_cpu_read(hard_watchdog_warn) == true) return; - if (hardlockup_panic) + /* + * 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 + } else { + spin_lock(&watchdog_output_lock); WARN(1, "Watchdog detected hard LOCKUP on cpu %d", this_cpu); + spin_unlock(&watchdog_output_lock); + } __this_cpu_write(hard_watchdog_warn, true); return; --------------010400080107020202000007--