clocksource: exynos_mct: Fix stall after CPU hotplugging

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).

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@samsung.com>
Change-Id: I3a1a23e2b970661b5f7c60fc633a7545aa80ed5e

diff --git a/drivers/clocksource/exynos_mct.c b/drivers/clocksource/exynos_mct.c
index 119917d..7b6ee77 100644 (file)
--- a/drivers/clocksource/exynos_mct.c
+++ b/drivers/clocksource/exynos_mct.c
@@ -345,7 +345,14 @@ 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);
 
@@ -377,23 +384,13 @@ 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)
@@ -401,6 +398,13 @@ 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);
@@ -463,7 +467,10 @@ static int __cpuinit exynos4_local_timer_setup(struct clock_event_device *evt)
 static void exynos4_local_timer_stop(struct clock_event_device *evt)
 {
        unsigned int cpu = smp_processor_id();
+       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)
                if (cpu == 0)
                        remove_irq(evt->irq, &mct_tick0_event_irq);