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

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Message-Id: <26cd375a8d7ef97db5f8d12ecda6ee6676aca211.1466484019.git.panand@redhat.com>
Date:	Tue, 21 Jun 2016 10:25:36 +0530
From:	Pratyush Anand <panand@...hat.com>
To:	mingo@...nel.org, alexandre.belloni@...e-electrons.com
Cc:	rtc-linux@...glegroups.com, linux-kernel@...r.kernel.org,
	prarit@...hat.com, Pratyush Anand <panand@...hat.com>,
	Alessandro Zummo <a.zummo@...ertech.it>
Subject: [PATCH RFC 2/2] rtc/rtc-cmos: Initialize software counters before irq is registered

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".

I am still clueless, how can an interrupt be raised before RTC is enabled.
But I do not have any idea about this device, so I am putting this patch as
RFC to get feedback from hpet/rtc-cmos developer.

I am initializing software counters in this patch so that LOCKUP could be
avoided. Even if it resolves the issue, I understand that proposed patch
may not be the best way to solve this issue.

Signed-off-by: Pratyush Anand <panand@...hat.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