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[PATCH V3 0/2] rtc-cmos: Workaround unwanted interrupt generation

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  [PATCH V3 0/2] rtc-cmos: Workaround unwanted interrupt generation Pratyush Anand <panand@redhat.com> - 2016-08-16 05:30 +0200
    [PATCH V3 2/2] rtc/rtc-cmos: Initialize software counters before irq is registered Pratyush Anand <panand@redhat.com> - 2016-08-16 05:40 +0200
    [PATCH V3 1/2] rtc/hpet: Factorize hpet_rtc_timer_init() Pratyush Anand <panand@redhat.com> - 2016-08-16 05:40 +0200

#1463377 — [PATCH V3 0/2] rtc-cmos: Workaround unwanted interrupt generation

We have observed on few machines with rtc-cmos devices that it generates
an interrupt before the hpet_rtc_timer_init() call is finished. This leads
to hpet_rtc_interrupt() being called before it is fully initialized.

Therefore the 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 set initializes hpet_default_delta and hpet_t1_cmp before
interrupt can be raised.

Changes since V2:
  - Improved commit log further
Changes since RFC:
  - Commit log of patches has been improved.

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

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#1463384 — [PATCH V3 2/2] rtc/rtc-cmos: Initialize software counters before irq is registered

We have observed on few x86 machines with rtc-cmos device that
hpet_rtc_interrupt() is called just after irq registration and before
cmos_do_probe() could call hpet_rtc_timer_init().

So, neither hpet_default_delta nor hpet_t1_cmp is initialized by the time
interrupt is raised in the given situation, and this results in NMI
watchdog LOCKUP.

It has only been observed sporadically on kdump secondary kernels.

See the call trace:
---<-snip->---
   27.913194] Kernel panic - not syncing: Watchdog detected hard LOCKUP on
cpu 0
[   27.915371] CPU: 0 PID: 1 Comm: swapper/0 Not tainted
3.10.0-342.el7.x86_64 #1
[   27.917503] Hardware name: HP ProLiant DL160 Gen8, BIOS J03 02/10/2014
[   27.919455]  ffffffff8186a728 0000000059c82488 ffff880034e05af0
ffffffff81637bd4
[   27.921870]  ffff880034e05b70 ffffffff8163144a 0000000000000010
ffff880034e05b80
[   27.924257]  ffff880034e05b20 0000000059c82488 0000000000000000
0000000000000000
[   27.926599] Call Trace:
[   27.927352]  <NMI>  [<ffffffff81637bd4>] dump_stack+0x19/0x1b
[   27.929080]  [<ffffffff8163144a>] panic+0xd8/0x1e7
[   27.930588]  [<ffffffff8111d3e0>] ? restart_watchdog_hrtimer+0x50/0x50
[   27.932502]  [<ffffffff8111d4a2>] watchdog_overflow_callback+0xc2/0xd0
[   27.934427]  [<ffffffff811612c1>] __perf_event_overflow+0xa1/0x250
[   27.936232]  [<ffffffff81161d94>] perf_event_overflow+0x14/0x20
[   27.937957]  [<ffffffff81032ae8>] intel_pmu_handle_irq+0x1e8/0x470
[   27.939799]  [<ffffffff8164164b>] perf_event_nmi_handler+0x2b/0x50
[   27.941649]  [<ffffffff81640d99>] nmi_handle.isra.0+0x69/0xb0
[   27.943348]  [<ffffffff81640f49>] do_nmi+0x169/0x340
[   27.944802]  [<ffffffff816401d3>] end_repeat_nmi+0x1e/0x2e
[   27.946424]  [<ffffffff81056ee5>] ? hpet_rtc_interrupt+0x85/0x380
[   27.948197]  [<ffffffff81056ee5>] ? hpet_rtc_interrupt+0x85/0x380
[   27.949992]  [<ffffffff81056ee5>] ? hpet_rtc_interrupt+0x85/0x380
[   27.951816]  <<EOE>>  <IRQ>  [<ffffffff8108f5a3>] ?
run_timer_softirq+0x43/0x340
[   27.954114]  [<ffffffff8111e24e>] handle_irq_event_percpu+0x3e/0x1e0
[   27.955962]  [<ffffffff8111e42d>] handle_irq_event+0x3d/0x60
[   27.957635]  [<ffffffff811210c7>] handle_edge_irq+0x77/0x130
[   27.959332]  [<ffffffff8101704f>] handle_irq+0xbf/0x150
[   27.960949]  [<ffffffff8164a86f>] do_IRQ+0x4f/0xf0
[   27.962434]  [<ffffffff8163faed>] common_interrupt+0x6d/0x6d
[   27.964101]  <EOI>  [<ffffffff8163f43b>] ?
_raw_spin_unlock_irqrestore+0x1b/0x40
[   27.966308]  [<fffff8111ff07>] __setup_irq+0x2a7/0x570
[   28.067859]  [<ffffffff81056e60>] ? hpet_cpuhp_notify+0x140/0x140
[   28.069709]  [<ffffffff8112032c>] request_threaded_irq+0xcc/0x170
[   28.071585]  [<ffffffff814b24a6>] cmos_do_probe+0x1e6/0x450
[   28.073240]  [<ffffffff814b2710>] ? cmos_do_probe+0x450/0x450
[   28.074911]  [<ffffffff814b27cb>] cmos_pnp_probe+0xbb/0xc0
[   28.076533]  [<ffffffff8139b245>] pnp_device_probe+0x65/0xd0
[   28.078198]  [<ffffffff813f8ca7>] driver_probe_device+0x87/0x390
[   28.079971]  [<ffffffff813f9083>] __driver_attach+0x93/0xa0
[   28.081660]  [<ffffffff813f8ff0>] ? __device_attach+0x40/0x40
[   28.083662]  [<ffffffff813f6a13>] bus_for_each_dev+0x73/0xc0
[   28.085370]  [<ffffffff813f86fe>] driver_attach+0x1e/0x20
[   28.086974]  [<ffffffff813f8250>] bus_add_driver+0x200/0x2d0
[   28.088634]  [<ffffffff81ade49a>] ? rtc_sysfs_init+0xe/0xe
[   28.090349]  [<ffffffff813f9704>] driver_register+0x64/0xf0
[   28.091989]  [<ffffffff8139b070>] pnp_register_driver+0x20/0x30
[   28.093707]  [<ffffffff81ade4ab>] cmos_init+0x11/0x71
---<-snip->---

The previous patch split hpet_rtc_timer_init into
hpet_rtc_timer_counter_init() and hpet_rtc_timer_enable().

Therefore, this patch moved hpet_rtc_timer_counter_init() before IRQ
registration, so that we can gracefully handle such spurious interrupts.

We were able to reproduce the problem in maximum 15 trials of kdump
secondary kernel boot on an hp-dl160gen8 machine without this patch.
However, more than 35 trials went fine after applying this patch.

Signed-off-by: Pratyush Anand <panand@redhat.com>
[dzickus@redhat.com: edited the patch's summary]
Signed-off-by: Don Zickus <dzickus@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 43745cac0141..089d987f2638 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;
@@ -707,6 +717,7 @@ 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;
 
@@ -729,7 +740,7 @@ 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

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#1463385 — [PATCH V3 1/2] rtc/hpet: Factorize hpet_rtc_timer_init()

We need the ability to support initialization of hpet_default_delta and
hpet_t1_cmp counters before irq can be enabled.

This patch splits hpet_rtc_timer_init() into two functions:
hpet_rtc_timer_counter_init() and hpet_rtc_timer_enable, so that the above
functionality can be achieved.

Next patch explains it's need in detail.

No functional change in this patch.

Signed-off-by: Pratyush Anand <panand@redhat.com>
[dzickus@redhat.com: edited the patch's summary]
Signed-off-by: Don Zickus <dzickus@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 ed16e58658a4..6f6d21059b1b 100644
--- a/arch/x86/kernel/hpet.c
+++ b/arch/x86/kernel/hpet.c
@@ -1074,14 +1074,12 @@ 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())
@@ -1106,6 +1104,22 @@ 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;
@@ -1115,6 +1129,21 @@ 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

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