Message-Id: <201006172136.AA00435@tamuki.linet.gr.jp>
Date:	Fri, 18 Jun 2010 06:36:31 +0900
From:	TAMUKI Shoichi <tamuki@...et.gr.jp>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Anton Blanchard <anton@...ba.org>,
	Andi Kleen <andi@...stfloor.org>,
	Andy Green <andy@...mcat.com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	TAMUKI Shoichi <tamuki@...et.gr.jp>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v3] panic: keep blinking in spite of long spin timer mode

To keep panic_timeout accuracy when running under a hypervisor, the
current implementation only spins on long time (1 second) calls to
mdelay.  That brings a good effect, but the problem is the keyboard
LEDs don't blink at all on that situation.

This patch changes to call to panic_blink_enter() between every mdelay
and keeps blinking in spite of long spin timer mode.

The default time to call to mdelay is 1ms.  It will be switched to
longer if the CONFIG_PANIC_LONGSPIN_TIMER kernel configuration option
is enabled.  This feature is helpful when running under a hypervisor.

Signed-off-by: TAMUKI Shoichi <tamuki@...et.gr.jp>
---
 Changes since v2.1:
 - get rid of panicblink= kernel parameter
 - introduce new kernel config option CONFIG_PANIC_LONGSPIN_TIMER

 Documentation/kernel-parameters.txt |    3 -
 arch/arm/mach-s3c2440/mach-gta02.c  |   17 +-----
 drivers/input/serio/i8042.c         |   25 +--------
 include/linux/kernel.h              |    2 
 init/Kconfig                        |   15 +++++
 kernel/panic.c                      |   68 ++++++++++++++++----------
 6 files changed, 68 insertions(+), 62 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index fa2f098..fd8a873 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -911,9 +911,6 @@ and is between 256 and 4096 characters. It is defined in the file
 			     controller
 	i8042.nopnp	[HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
 			     controllers
-	i8042.panicblink=
-			[HW] Frequency with which keyboard LEDs should blink
-			     when kernel panics (default is 0.5 sec)
 	i8042.reset	[HW] Reset the controller during init and cleanup
 	i8042.unlock	[HW] Unlock (ignore) the keylock
 
diff --git a/arch/arm/mach-s3c2440/mach-gta02.c b/arch/arm/mach-s3c2440/mach-gta02.c
index 9e39faa..deaabe8 100644
--- a/arch/arm/mach-s3c2440/mach-gta02.c
+++ b/arch/arm/mach-s3c2440/mach-gta02.c
@@ -90,24 +90,17 @@
 static struct pcf50633 *gta02_pcf;
 
 /*
- * This gets called every 1ms when we paniced.
+ * This gets called frequently when we paniced.
  */
 
-static long gta02_panic_blink(long count)
+static long gta02_panic_blink(int state)
 {
 	long delay = 0;
-	static long last_blink;
-	static char led;
+	char led;
 
-	/* Fast blink: 200ms period. */
-	if (count - last_blink < 100)
-		return 0;
-
-	led ^= 1;
+	led = (state) ? 1 : 0;
 	gpio_direction_output(GTA02_GPIO_AUX_LED, led);
 
-	last_blink = count;
-
 	return delay;
 }
 
@@ -556,7 +549,7 @@ static void gta02_poweroff(void)
 
 static void __init gta02_machine_init(void)
 {
-	/* Set the panic callback to make AUX LED blink at ~5Hz. */
+	/* Set the panic callback to turn AUX LED on or off. */
 	panic_blink = gta02_panic_blink;
 
 	s3c_pm_init();
diff --git a/drivers/input/serio/i8042.c b/drivers/input/serio/i8042.c
index 6440a8f..c32d9b3 100644
--- a/drivers/input/serio/i8042.c
+++ b/drivers/input/serio/i8042.c
@@ -61,10 +61,6 @@ static bool i8042_noloop;
 module_param_named(noloop, i8042_noloop, bool, 0);
 MODULE_PARM_DESC(noloop, "Disable the AUX Loopback command while probing for the AUX port");
 
-static unsigned int i8042_blink_frequency = 500;
-module_param_named(panicblink, i8042_blink_frequency, uint, 0600);
-MODULE_PARM_DESC(panicblink, "Frequency with which keyboard LEDs should blink when kernel panics");
-
 #ifdef CONFIG_X86
 static bool i8042_dritek;
 module_param_named(dritek, i8042_dritek, bool, 0);
@@ -1032,8 +1028,8 @@ static void i8042_controller_reset(void)
 
 
 /*
- * i8042_panic_blink() will flash the keyboard LEDs and is called when
- * kernel panics. Flashing LEDs is useful for users running X who may
+ * i8042_panic_blink() will turn the keyboard LEDs on or off and is called
+ * when kernel panics. Flashing LEDs is useful for users running X who may
  * not see the console and will help distingushing panics from "real"
  * lockups.
  *
@@ -1043,22 +1039,12 @@ static void i8042_controller_reset(void)
 
 #define DELAY do { mdelay(1); if (++delay > 10) return delay; } while(0)
 
-static long i8042_panic_blink(long count)
+static long i8042_panic_blink(int state)
 {
 	long delay = 0;
-	static long last_blink;
-	static char led;
-
-	/*
-	 * We expect frequency to be about 1/2s. KDB uses about 1s.
-	 * Make sure they are different.
-	 */
-	if (!i8042_blink_frequency)
-		return 0;
-	if (count - last_blink < i8042_blink_frequency)
-		return 0;
+	char led;
 
-	led ^= 0x01 | 0x04;
+	led = (state) ? 0x01 | 0x04 : 0;
 	while (i8042_read_status() & I8042_STR_IBF)
 		DELAY;
 	dbg("%02x -> i8042 (panic blink)", 0xed);
@@ -1071,7 +1057,6 @@ static long i8042_panic_blink(long count)
 	dbg("%02x -> i8042 (panic blink)", led);
 	i8042_write_data(led);
 	DELAY;
-	last_blink = count;
 	return delay;
 }
 
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 8317ec4..7d4552a 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -172,7 +172,7 @@ static inline void might_fault(void)
 #endif
 
 extern struct atomic_notifier_head panic_notifier_list;
-extern long (*panic_blink)(long time);
+extern long (*panic_blink)(int state);
 NORET_TYPE void panic(const char * fmt, ...)
 	__attribute__ ((NORET_AND format (printf, 1, 2))) __cold;
 extern void oops_enter(void);
diff --git a/init/Kconfig b/init/Kconfig
index 05e932e..b37f6a6 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1171,6 +1171,21 @@ config SLOW_WORK_DEBUG
 
 	  See Documentation/slow-work.txt.
 
+config PANIC_LONGSPIN_TIMER
+	bool "Enable long spin timer mode when kernel panics"
+	default n
+	help
+	  On certain shared processor partitions, panic_timeout will be
+	  wildly inaccurate (a 3 minute panic_timeout taking 30 minutes).
+
+	  The fact is we loop on mdelay(1) and with a 1ms in 10ms hyper-
+	  visor timeslice each of these will take 10ms (i.e. 10x) longer.
+	  If you say Y here, spin on long time calls to mdelay to avoid
+	  this.
+
+	  This feature is helpful when running under such a special case
+	  like a hypervisor.  If unsure, say N.
+
 endmenu		# General setup
 
 config HAVE_GENERIC_DMA_COHERENT
diff --git a/kernel/panic.c b/kernel/panic.c
index 3b16cd9..769aa85 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -24,6 +24,14 @@
 #include <linux/nmi.h>
 #include <linux/dmi.h>
 
+#ifdef CONFIG_PANIC_LONGSPIN_TIMER
+#define PANIC_TIMER_STEP 240
+#define PANIC_BLINK_SPD 5
+#else
+#define PANIC_TIMER_STEP 1
+#define PANIC_BLINK_SPD 20
+#endif
+
 int panic_on_oops;
 static unsigned long tainted_mask;
 static int pause_on_oops;
@@ -36,34 +44,37 @@ ATOMIC_NOTIFIER_HEAD(panic_notifier_list);
 
 EXPORT_SYMBOL(panic_notifier_list);
 
+static long no_blink(int state)
+{
+	return 0;
+}
+
 /* Returns how long it waited in ms */
-long (*panic_blink)(long time);
+long (*panic_blink)(int state);
 EXPORT_SYMBOL(panic_blink);
 
-static void panic_blink_one_second(void)
+static long panic_blink_enter(long count)
 {
-	static long i = 0, end;
-
-	if (panic_blink) {
-		end = i + MSEC_PER_SEC;
-
-		while (i < end) {
-			i += panic_blink(i);
-			mdelay(1);
-			i++;
-		}
+	int len;
+	long delay = 0;
+	static int state = 1;
+	static int first = 1;
+	static long next_count;
+
+	len = 3600 / PANIC_BLINK_SPD;
+	if (!first && count - next_count < 0)
+		return 0;
+	if (state) {
+		delay += panic_blink(0);
+		state = 0;
+		if (first)
+			first = 0;
 	} else {
-		/*
-		 * When running under a hypervisor a small mdelay may get
-		 * rounded up to the hypervisor timeslice. For example, with
-		 * a 1ms in 10ms hypervisor timeslice we might inflate a
-		 * mdelay(1) loop by 10x.
-		 *
-		 * If we have nothing to blink, spin on 1 second calls to
-		 * mdelay to avoid this.
-		 */
-		mdelay(MSEC_PER_SEC);
+		delay += panic_blink(1);
+		state = 1;
 	}
+	next_count = count + len;
+	return delay;
 }
 
 /**
@@ -117,6 +128,9 @@ NORET_TYPE void panic(const char * fmt, ...)
 
 	bust_spinlocks(0);
 
+	if (!panic_blink)
+		panic_blink = no_blink;
+
 	if (panic_timeout > 0) {
 		/*
 		 * Delay timeout seconds before rebooting the machine.
@@ -124,9 +138,10 @@ NORET_TYPE void panic(const char * fmt, ...)
 		 */
 		printk(KERN_EMERG "Rebooting in %d seconds..", panic_timeout);
 
-		for (i = 0; i < panic_timeout; i++) {
+		for (i = 0; i < panic_timeout * 1000; i += PANIC_TIMER_STEP) {
 			touch_nmi_watchdog();
-			panic_blink_one_second();
+			i += panic_blink_enter(i);
+			mdelay(PANIC_TIMER_STEP);
 		}
 		/*
 		 * This will not be a clean reboot, with everything
@@ -152,9 +167,10 @@ NORET_TYPE void panic(const char * fmt, ...)
 	}
 #endif
 	local_irq_enable();
-	while (1) {
+	for (i = 0; ; i += PANIC_TIMER_STEP) {
 		touch_softlockup_watchdog();
-		panic_blink_one_second();
+		i += panic_blink_enter(i);
+		mdelay(PANIC_TIMER_STEP);
 	}
 }
 
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