[PATCH V2 0/2] rtc-cmos: Workaround unwanted interrupt generation

[PATCH V2 0/2] rtc-cmos: Workaround unwanted interrupt generation

[Pratyush Anand]

We have observed on few machines with rtc-cmos device that
hpet_rtc_interrupt() is called before cmos_do_probe() could call
hpet_rtc_timer_init(). It has not been observed during normal boot/reboot
of machines. It *sometime* happens when system is booted with kdump
secondary kernel. So, neither hpet_default_delta nor hpet_t1_cmp is
initialized by the time interrupt is raised in the given situation.
Therefore while loop of hpet_cnt_ahead() in hpet_rtc_timer_reinit() never
completes. This leads to "NMI watchdog: Watchdog detected hard LOCKUP on
cpu 0".

These patch set initializes hpet_default_delta and hpet_t1_cmp before
interrupt can be raised.

Changes since RFC:
  - Commit log of patches has been improved.
  - RFCs were here: https://lkml.org/lkml/2016/6/21/35

Pratyush Anand (2):
  rtc/hpet: Factorize hpet_rtc_timer_init()
  rtc/rtc-cmos: Initialize software counters before irq is registered

 arch/x86/include/asm/hpet.h |  2 ++
 arch/x86/kernel/hpet.c      | 41 +++++++++++++++++++++++++++++++++++------
 drivers/rtc/rtc-cmos.c      | 13 ++++++++++++-
 3 files changed, 49 insertions(+), 7 deletions(-)

-- 
2.5.5

[PATCH V2 1/2] rtc/hpet: Factorize hpet_rtc_timer_init()

[Pratyush Anand]

We have observed on few machines with rtc-cmos device that
hpet_rtc_interrupt() is called before cmos_do_probe() could call
hpet_rtc_timer_init(). It has not been observed during normal boot/reboot
of machines. It *sometime* happens when system is booted with kdump
secondary kernel. So, neither hpet_default_delta nor hpet_t1_cmp is
initialized by the time interrupt is raised in the given situation.
Therefore while loop of hpet_cnt_ahead() in hpet_rtc_timer_reinit() never
completes. This leads to "NMI watchdog: Watchdog detected hard LOCKUP on
cpu 0".

This patch factorize hpet_rtc_timer_init(), so that counter can be
initialized before irq is registered.

No functional change in this patch.

Signed-off-by: Pratyush Anand <panand@redhat.com>
---
 arch/x86/include/asm/hpet.h |  2 ++
 arch/x86/kernel/hpet.c      | 41 +++++++++++++++++++++++++++++++++++------
 2 files changed, 37 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/hpet.h b/arch/x86/include/asm/hpet.h
index cc285ec4b2c1..8eecb31bebcb 100644
--- a/arch/x86/include/asm/hpet.h
+++ b/arch/x86/include/asm/hpet.h
@@ -96,6 +96,8 @@ extern int hpet_set_alarm_time(unsigned char hrs, unsigned char min,
 			       unsigned char sec);
 extern int hpet_set_periodic_freq(unsigned long freq);
 extern int hpet_rtc_dropped_irq(void);
+extern int hpet_rtc_timer_counter_init(void);
+extern int hpet_rtc_timer_enable(void);
 extern int hpet_rtc_timer_init(void);
 extern irqreturn_t hpet_rtc_interrupt(int irq, void *dev_id);
 extern int hpet_register_irq_handler(rtc_irq_handler handler);
diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
index 3d747070fe67..c9da694ff236 100644
--- a/arch/x86/kernel/hpet.c
+++ b/arch/x86/kernel/hpet.c
@@ -1075,14 +1075,12 @@ void hpet_unregister_irq_handler(rtc_irq_handler handler)
 EXPORT_SYMBOL_GPL(hpet_unregister_irq_handler);
 
 /*
- * Timer 1 for RTC emulation. We use one shot mode, as periodic mode
- * is not supported by all HPET implementations for timer 1.
- *
- * hpet_rtc_timer_init() is called when the rtc is initialized.
+ * hpet_rtc_timer_counter_init() is called before interrupt can be
+ * registered
  */
-int hpet_rtc_timer_init(void)
+int hpet_rtc_timer_counter_init(void)
 {
-	unsigned int cfg, cnt, delta;
+	unsigned int cnt, delta;
 	unsigned long flags;
 
 	if (!is_hpet_enabled())
@@ -1107,6 +1105,22 @@ int hpet_rtc_timer_init(void)
 	hpet_writel(cnt, HPET_T1_CMP);
 	hpet_t1_cmp = cnt;
 
+	local_irq_restore(flags);
+
+	return 1;
+}
+EXPORT_SYMBOL_GPL(hpet_rtc_timer_counter_init);
+
+/*
+ * hpet_rtc_timer_enable() is called during RTC initialization
+ */
+int hpet_rtc_timer_enable(void)
+{
+	unsigned int cfg;
+	unsigned long flags;
+
+	local_irq_save(flags);
+
 	cfg = hpet_readl(HPET_T1_CFG);
 	cfg &= ~HPET_TN_PERIODIC;
 	cfg |= HPET_TN_ENABLE | HPET_TN_32BIT;
@@ -1116,6 +1130,21 @@ int hpet_rtc_timer_init(void)
 
 	return 1;
 }
+EXPORT_SYMBOL_GPL(hpet_rtc_timer_enable);
+
+/*
+ * Timer 1 for RTC emulation. We use one shot mode, as periodic mode
+ * is not supported by all HPET implementations for timer 1.
+ *
+ * hpet_rtc_timer_init() is called when the rtc is initialized.
+ */
+int hpet_rtc_timer_init(void)
+{
+	if (!hpet_rtc_timer_counter_init())
+		return 0;
+
+	return hpet_rtc_timer_enable();
+}
 EXPORT_SYMBOL_GPL(hpet_rtc_timer_init);
 
 static void hpet_disable_rtc_channel(void)
-- 
2.5.5

[PATCH V2 2/2] rtc/rtc-cmos: Initialize software counters before irq is registered

[Pratyush Anand]

We have observed on few machines with rtc-cmos device that
hpet_rtc_interrupt() is called before cmos_do_probe() could call
hpet_rtc_timer_init(). It has not been observed during normal boot/reboot
of machines. It *sometime* happens when system is booted with kdump
secondary kernel. So, neither hpet_default_delta nor hpet_t1_cmp is
initialized by the time interrupt is raised in the given situation.
Therefore while loop of hpet_cnt_ahead() in hpet_rtc_timer_reinit() never
completes. This leads to "NMI watchdog: Watchdog detected hard LOCKUP on
cpu 0".

Software counters are being initialized in this patch so that LOCKUP could
be avoided.

Signed-off-by: Pratyush Anand <panand@redhat.com>
---
 drivers/rtc/rtc-cmos.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
index fbe9c72438e1..101dc948295f 100644
--- a/drivers/rtc/rtc-cmos.c
+++ b/drivers/rtc/rtc-cmos.c
@@ -129,6 +129,16 @@ static inline int hpet_rtc_dropped_irq(void)
 	return 0;
 }
 
+static inline int hpet_rtc_timer_counter_init(void)
+{
+	return 0;
+}
+
+static inline int hpet_rtc_timer_enable(void)
+{
+	return 0;
+}
+
 static inline int hpet_rtc_timer_init(void)
 {
 	return 0;
@@ -710,6 +720,7 @@ cmos_do_probe(struct device *dev, struct resource *ports, int rtc_irq)
 		goto cleanup1;
 	}
 
+	hpet_rtc_timer_counter_init();
 	if (is_valid_irq(rtc_irq)) {
 		irq_handler_t rtc_cmos_int_handler;
 
@@ -732,7 +743,7 @@ cmos_do_probe(struct device *dev, struct resource *ports, int rtc_irq)
 			goto cleanup1;
 		}
 	}
-	hpet_rtc_timer_init();
+	hpet_rtc_timer_enable();
 
 	/* export at least the first block of NVRAM */
 	nvram.size = address_space - NVRAM_OFFSET;
-- 
2.5.5