[PATCH] tick/nohz: Fix the intention to stop full tick for offline CPU

[Wanpeng Li]

From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>

Interrupt exit is the place to stop the tick: it happens after all 
events happening before and during the irq which are liable to update 
the dependency on the tick occurred. However, tick_nohz_stop_sched_tick() 
try to stop the full tick instead of bailing out in advance. 

As a result: 

WARNING: CPU: 3 PID: 31 at kernel/irq_work.c:124 irq_work_needs_cpu+0x86/0x90
CPU: 3 PID: 31 Comm: migration/3 Not tainted 4.8.0-rc5+ #46
Call Trace:
 <IRQ>  [<ffffffffb94477c9>] dump_stack+0x99/0xd0
 [<ffffffffb908d581>] __warn+0xd1/0xf0
 [<ffffffffb908d66d>] warn_slowpath_null+0x1d/0x20
 [<ffffffffb91a7446>] irq_work_needs_cpu+0x86/0x90
 [<ffffffffb912cbed>] tick_nohz_stop_sched_tick+0x2ad/0x430
 [<ffffffffb912d75e>] ? tick_nohz_irq_exit+0x10e/0x150
 [<ffffffffb906de05>] ? kvm_clock_read+0x25/0x30
 [<ffffffffb912d75e>] tick_nohz_irq_exit+0x10e/0x150
 [<ffffffffb9094a31>] irq_exit+0x81/0xf0
 [<ffffffffb98ca4cc>] do_IRQ+0x6c/0x120
 [<ffffffffb98c83d6>] common_interrupt+0x96/0x96
 <EOI>  [<ffffffffb9153fb2>] ? multi_cpu_stop+0xa2/0x160
 [<ffffffffb9153f10>] ? cpu_stop_park+0x40/0x40
 [<ffffffffb9153e44>] cpu_stopper_thread+0x74/0x100
 [<ffffffffb90b7e77>] smpboot_thread_fn+0x117/0x1d0
 [<ffffffffb90b7d60>] ? sort_range+0x30/0x30
 [<ffffffffb90b4111>] kthread+0x101/0x120
 [<ffffffffb90dea6d>] ? complete+0x1d/0x50
 [<ffffffffb98c7c8f>] ret_from_fork+0x1f/0x40
 [<ffffffffb90b4010>] ? kthread_create_on_node+0x250/0x250

Commit f7ea0fd639c2c4 (tick: Don't invoke tick_nohz_stop_sched_tick() if 
the cpu is offline) fixes stop idle tick for offline cpu, this patch adds 
the similar method to fix the intention to stop full tick for offline cpu.

Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
---
 kernel/time/tick-sched.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 2ec7c00..3bcb61b 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -186,10 +186,13 @@ static bool check_tick_dependency(atomic_t *dep)
 	return false;
 }
 
-static bool can_stop_full_tick(struct tick_sched *ts)
+static bool can_stop_full_tick(int cpu, struct tick_sched *ts)
 {
 	WARN_ON_ONCE(!irqs_disabled());
 
+	if (unlikely(!cpu_online(cpu)))
+		return false;
+
 	if (check_tick_dependency(&tick_dep_mask))
 		return false;
 
@@ -843,7 +846,7 @@ static void tick_nohz_full_update_tick(struct tick_sched *ts)
 	if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
 		return;
 
-	if (can_stop_full_tick(ts))
+	if (can_stop_full_tick(cpu, ts))
 		tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
 	else if (ts->tick_stopped)
 		tick_nohz_restart_sched_tick(ts, ktime_get());
-- 
1.9.1