[PATCH] clocksource: exynos_mct: Fix stall after CPU hotplugging
From: Krzysztof Kozlowski
Date: Tue Mar 25 2014 - 06:41:51 EST
Fix stall after hotplugging CPU1. The stall was a result of starting the
CPU1 local timer not in L1 timer but in L0 (which is used by CPU0).
Trigger:
$ echo 0 > /sys/bus/cpu/devices/cpu1/online && echo 1 > /sys/bus/cpu/devices/cpu1/online
Stall information:
[ 530.045259] INFO: rcu_preempt detected stalls on CPUs/tasks:
[ 530.045618] 1: (6 GPs behind) idle=6d0/0/0 softirq=369/369
[ 530.050987] (detected by 0, t=6589 jiffies, g=33, c=32, q=0)
[ 530.056721] Task dump for CPU 1:
[ 530.059928] swapper/1 R running 0 0 1 0x00001000
[ 530.066377] [<c0524e14>] (__schedule+0x414/0x9b4) from [<c00b6610>] (rcu_idle_enter+0x18/0x38)
[ 530.074955] [<c00b6610>] (rcu_idle_enter+0x18/0x38) from [<c0079a18>] (cpu_startup_entry+0x60/0x3bc)
[ 530.084069] [<c0079a18>] (cpu_startup_entry+0x60/0x3bc) from [<c0517d34>] (secondary_start_kernel+0x164/0x1a0)
[ 530.094029] [<c0517d34>] (secondary_start_kernel+0x164/0x1a0) from [<40517244>] (0x40517244)
The timers for CPU1 were missed:
[ 591.668436] cpu: 1
[ 591.670430] clock 0:
[ 591.672691] .base: c0ab7750
[ 591.676160] .index: 0
[ 591.679025] .resolution: 1 nsecs
[ 591.682404] .get_time: ktime_get
[ 591.685970] .offset: 0 nsecs
[ 591.689349] active timers:
[ 591.692045] #0: <dfb51f40>, hrtimer_wakeup, S:01
[ 591.696759] # expires at 454687834257-454687884257 nsecs [in -136770537232 to -136770487232 nsecs]
And the event_handler for next event was wrong:
[ 591.917120] Tick Device: mode: 1
[ 591.920676] Per CPU device: 0
[ 591.923621] Clock Event Device: mct_tick0
[ 591.927623] max_delta_ns: 178956969027
[ 591.931613] min_delta_ns: 1249
[ 591.934913] mult: 51539608
[ 591.938557] shift: 32
[ 591.941681] mode: 3
[ 591.944724] next_event: 595025000000 nsecs
[ 591.949227] set_next_event: exynos4_tick_set_next_event
[ 591.954522] set_mode: exynos4_tick_set_mode
[ 591.959296] event_handler: hrtimer_interrupt
[ 591.963730] retries: 0
[ 591.966761]
[ 591.968245] Tick Device: mode: 0
[ 591.971801] Per CPU device: 1
[ 591.974746] Clock Event Device: mct_tick1
[ 591.978750] max_delta_ns: 178956969027
[ 591.982739] min_delta_ns: 1249
[ 591.986037] mult: 51539608
[ 591.989681] shift: 32
[ 591.992806] mode: 3
[ 591.995848] next_event: 453685000000 nsecs
[ 592.000353] set_next_event: exynos4_tick_set_next_event
[ 592.005648] set_mode: exynos4_tick_set_mode
[ 592.010421] event_handler: tick_handle_periodic
[ 592.015115] retries: 0
[ 592.018145]
After turning off the CPU1, the MCT L1 local timer was disabled but the
interrupt was not cleared. Turning on the CPU1 enabled the IRQ
with setup_irq() but, before setting affinity to CPU1, the pending L1 timer
interrupt was processed by CPU0 in exynos4_mct_tick_isr().
The ISR then called event handler which set up the next timer event for
current CPU (CPU0). Therefore the MCT L1 timer wasn't actually started.
Fix the stall by:
1. Setting next timer event not on current CPU but on the CPU indicated
by cpumask in 'clock_event_device'.
2. Clearing the timer interrupt upon stopping the local timer.
The patch also moves around the call to exynos4_mct_tick_stop() but this
is done only for the code readability as it is not essential for the fix.
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@xxxxxxxxxxx>
---
drivers/clocksource/exynos_mct.c | 33 ++++++++++++++++++++-------------
1 file changed, 20 insertions(+), 13 deletions(-)
diff --git a/drivers/clocksource/exynos_mct.c b/drivers/clocksource/exynos_mct.c
index 48f76bc05da0..0b49b09dd1a9 100644
--- a/drivers/clocksource/exynos_mct.c
+++ b/drivers/clocksource/exynos_mct.c
@@ -339,7 +339,14 @@ static void exynos4_mct_tick_start(unsigned long cycles,
static int exynos4_tick_set_next_event(unsigned long cycles,
struct clock_event_device *evt)
{
- struct mct_clock_event_device *mevt = this_cpu_ptr(&percpu_mct_tick);
+ /*
+ * In case of hotplugging non-boot CPU, the set_next_event could be
+ * called on CPU0 by ISR before IRQ affinity is set to proper CPU.
+ * Thus for accessing proper MCT Lx timer, 'per_cpu' for cpumask
+ * in event must be used instead of 'this_cpu_ptr'.
+ */
+ struct mct_clock_event_device *mevt = &per_cpu(percpu_mct_tick,
+ cpumask_first(evt->cpumask));
exynos4_mct_tick_start(cycles, mevt);
@@ -371,23 +378,13 @@ static inline void exynos4_tick_set_mode(enum clock_event_mode mode,
static int exynos4_mct_tick_clear(struct mct_clock_event_device *mevt)
{
- struct clock_event_device *evt = &mevt->evt;
-
- /*
- * This is for supporting oneshot mode.
- * Mct would generate interrupt periodically
- * without explicit stopping.
- */
- if (evt->mode != CLOCK_EVT_MODE_PERIODIC)
- exynos4_mct_tick_stop(mevt);
-
/* Clear the MCT tick interrupt */
if (__raw_readl(reg_base + mevt->base + MCT_L_INT_CSTAT_OFFSET) & 1) {
exynos4_mct_write(0x1, mevt->base + MCT_L_INT_CSTAT_OFFSET);
return 1;
- } else {
- return 0;
}
+
+ return 0;
}
static irqreturn_t exynos4_mct_tick_isr(int irq, void *dev_id)
@@ -395,6 +392,13 @@ static irqreturn_t exynos4_mct_tick_isr(int irq, void *dev_id)
struct mct_clock_event_device *mevt = dev_id;
struct clock_event_device *evt = &mevt->evt;
+ /*
+ * This is for supporting oneshot mode.
+ * Mct would generate interrupt periodically
+ * without explicit stopping.
+ */
+ if (evt->mode != CLOCK_EVT_MODE_PERIODIC)
+ exynos4_mct_tick_stop(mevt);
exynos4_mct_tick_clear(mevt);
evt->event_handler(evt);
@@ -441,7 +445,10 @@ static int exynos4_local_timer_setup(struct clock_event_device *evt)
static void exynos4_local_timer_stop(struct clock_event_device *evt)
{
+ struct mct_clock_event_device *mevt = this_cpu_ptr(&percpu_mct_tick);
+
evt->set_mode(CLOCK_EVT_MODE_UNUSED, evt);
+ exynos4_mct_tick_clear(mevt);
if (mct_int_type == MCT_INT_SPI)
free_irq(evt->irq, this_cpu_ptr(&percpu_mct_tick));
else
--
1.7.9.5
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