[PATCH tip/core/rcu 09/12] idle: Prevent late-arriving interrupts from disrupting offline

["Paul E. McKenney" <paulmck@linux.ibm.com>]

From: Peter Zijlstra <peterz@infradead.org>

Scheduling-clock interrupts can arrive late in the CPU-offline process,
after idle entry and the subsequent call to cpuhp_report_idle_dead().
Once execution passes the call to rcu_report_dead(), RCU is ignoring
the CPU, which results in lockdep complaints when the interrupt handler
uses RCU:

------------------------------------------------------------------------

=============================
WARNING: suspicious RCU usage
5.2.0-rc1+ #681 Not tainted
-----------------------------
kernel/sched/fair.c:9542 suspicious rcu_dereference_check() usage!

other info that might help us debug this:

RCU used illegally from offline CPU!
rcu_scheduler_active = 2, debug_locks = 1
no locks held by swapper/5/0.

stack backtrace:
CPU: 5 PID: 0 Comm: swapper/5 Not tainted 5.2.0-rc1+ #681
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS Bochs 01/01/2011
Call Trace:
 <IRQ>
 dump_stack+0x5e/0x8b
 trigger_load_balance+0xa8/0x390
 ? tick_sched_do_timer+0x60/0x60
 update_process_times+0x3b/0x50
 tick_sched_handle+0x2f/0x40
 tick_sched_timer+0x32/0x70
 __hrtimer_run_queues+0xd3/0x3b0
 hrtimer_interrupt+0x11d/0x270
 ? sched_clock_local+0xc/0x74
 smp_apic_timer_interrupt+0x79/0x200
 apic_timer_interrupt+0xf/0x20
 </IRQ>
RIP: 0010:delay_tsc+0x22/0x50
Code: ff 0f 1f 80 00 00 00 00 65 44 8b 05 18 a7 11 48 0f ae e8 0f 31 48 89 d6 48 c1 e6 20 48 09 c6 eb 0e f3 90 65 8b 05 fe a6 11 48 <41> 39 c0 75 18 0f ae e8 0f 31 48 c1 e2 20 48 09 c2 48 89 d0 48 29
RSP: 0000:ffff8f92c0157ed0 EFLAGS: 00000212 ORIG_RAX: ffffffffffffff13
RAX: 0000000000000005 RBX: ffff8c861f356400 RCX: ffff8f92c0157e64
RDX: 000000321214c8cc RSI: 00000032120daa7f RDI: 0000000000260f15
RBP: 0000000000000005 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000001 R12: 0000000000000000
R13: 0000000000000000 R14: ffff8c861ee18000 R15: ffff8c861ee18000
 cpuhp_report_idle_dead+0x31/0x60
 do_idle+0x1d5/0x200
 ? _raw_spin_unlock_irqrestore+0x2d/0x40
 cpu_startup_entry+0x14/0x20
 start_secondary+0x151/0x170
 secondary_startup_64+0xa4/0xb0

------------------------------------------------------------------------

This happens rarely, but can be forced by happen more often by
placing delays in cpuhp_report_idle_dead() following the call to
rcu_report_dead().  With this in place, the following rcutorture
scenario reproduces the problem within a few minutes:

tools/testing/selftests/rcutorture/bin/kvm.sh --cpus 8 --duration 5 --kconfig "CONFIG_DEBUG_LOCK_ALLOC=y CONFIG_PROVE_LOCKING=y" --configs "TREE04"

This commit uses the crude but effective expedient of moving the disabling
of interrupts within the idle loop to precede the cpu_is_offline()
check.  It also invokes tick_nohz_idle_stop_tick() instead of
tick_nohz_idle_stop_tick_protected() to shut off the scheduling-clock
interrupt, and then removes the latter because there are no other callers.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
---
 include/linux/tick.h | 10 ----------
 kernel/sched/idle.c  |  5 +++--
 2 files changed, 3 insertions(+), 12 deletions(-)

diff --git a/include/linux/tick.h b/include/linux/tick.h
index f92a10b5e112..196a0a7bfc4f 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -134,14 +134,6 @@ extern unsigned long tick_nohz_get_idle_calls(void);
 extern unsigned long tick_nohz_get_idle_calls_cpu(int cpu);
 extern u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time);
 extern u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time);
-
-static inline void tick_nohz_idle_stop_tick_protected(void)
-{
-	local_irq_disable();
-	tick_nohz_idle_stop_tick();
-	local_irq_enable();
-}
-
 #else /* !CONFIG_NO_HZ_COMMON */
 #define tick_nohz_enabled (0)
 static inline int tick_nohz_tick_stopped(void) { return 0; }
@@ -164,8 +156,6 @@ static inline ktime_t tick_nohz_get_sleep_length(ktime_t *delta_next)
 }
 static inline u64 get_cpu_idle_time_us(int cpu, u64 *unused) { return -1; }
 static inline u64 get_cpu_iowait_time_us(int cpu, u64 *unused) { return -1; }
-
-static inline void tick_nohz_idle_stop_tick_protected(void) { }
 #endif /* !CONFIG_NO_HZ_COMMON */
 
 #ifdef CONFIG_NO_HZ_FULL
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 80940939b733..e4bc4aa739b8 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -241,13 +241,14 @@ static void do_idle(void)
 		check_pgt_cache();
 		rmb();
 
+		local_irq_disable();
+
 		if (cpu_is_offline(cpu)) {
-			tick_nohz_idle_stop_tick_protected();
+			tick_nohz_idle_stop_tick();
 			cpuhp_report_idle_dead();
 			arch_cpu_idle_dead();
 		}
 
-		local_irq_disable();
 		arch_cpu_idle_enter();
 
 		/*
-- 
2.17.1