[GIT PULL] nohz: Fix warning with perf on full dynticks

[Frederic Weisbecker]

Ingo,

Please pull the timers/urgent branch that can be found at:

git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
	timers/urgent

HEAD: 40bea039593dfc7f3f9814dab844f6db43ae580b

Summary:

* A patch merged in this merge window turned the nohz full kick to
become NMI-unsafe. But perf needs to use this kick from NMIs.
This patch fixes the issue by restoring the old NMI-safe internals of
the API.

Thanks,
	Frederic
---

Frederic Weisbecker (1):
      nohz: Restore NMI safe local irq work for local nohz kick


 include/linux/tick.h     |  7 +------
 kernel/time/tick-sched.c | 14 ++++++++++++++
 2 files changed, 15 insertions(+), 6 deletions(-)

---
commit 40bea039593dfc7f3f9814dab844f6db43ae580b
Author: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Date:   Wed Aug 13 18:50:16 2014 +0200

    nohz: Restore NMI safe local irq work for local nohz kick
    
    The local nohz kick is currently used by perf which needs it to be
    NMI-safe. Recent commit though (7d1311b93e58ed55f3a31cc8f94c4b8fe988a2b9)
    changed its implementation to fire the local kick using the remote kick
    API. It was convenient to make the code more generic but the remote kick
    isn't NMI-safe.
    
    As a result:
    
    	WARNING: CPU: 3 PID: 18062 at kernel/irq_work.c:72 irq_work_queue_on+0x11e/0x140()
    	CPU: 3 PID: 18062 Comm: trinity-subchil Not tainted 3.16.0+ #34
    	0000000000000009 00000000903774d1 ffff880244e06c00 ffffffff9a7f1e37
    	0000000000000000 ffff880244e06c38 ffffffff9a0791dd ffff880244fce180
    	0000000000000003 ffff880244e06d58 ffff880244e06ef8 0000000000000000
    	Call Trace:
    	<NMI>  [<ffffffff9a7f1e37>] dump_stack+0x4e/0x7a
    	[<ffffffff9a0791dd>] warn_slowpath_common+0x7d/0xa0
    	[<ffffffff9a07930a>] warn_slowpath_null+0x1a/0x20
    	[<ffffffff9a17ca1e>] irq_work_queue_on+0x11e/0x140
    	[<ffffffff9a10a2c7>] tick_nohz_full_kick_cpu+0x57/0x90
    	[<ffffffff9a186cd5>] __perf_event_overflow+0x275/0x350
    	[<ffffffff9a184f80>] ? perf_event_task_disable+0xa0/0xa0
    	[<ffffffff9a01a4cf>] ? x86_perf_event_set_period+0xbf/0x150
    	[<ffffffff9a187934>] perf_event_overflow+0x14/0x20
    	[<ffffffff9a020386>] intel_pmu_handle_irq+0x206/0x410
    	[<ffffffff9a0b54d3>] ? arch_vtime_task_switch+0x63/0x130
    	[<ffffffff9a01937b>] perf_event_nmi_handler+0x2b/0x50
    	[<ffffffff9a007b72>] nmi_handle+0xd2/0x390
    	[<ffffffff9a007aa5>] ? nmi_handle+0x5/0x390
    	[<ffffffff9a0d131b>] ? lock_release+0xab/0x330
    	[<ffffffff9a008062>] default_do_nmi+0x72/0x1c0
    	[<ffffffff9a0c925f>] ? cpuacct_account_field+0xcf/0x200
    	[<ffffffff9a008268>] do_nmi+0xb8/0x100
    
    Lets fix this by restoring the use of local irq work for the nohz local
    kick.
    
    Reported-by: Catalin Iacob <iacobcatalin@xxxxxxxxx>
    Reported-and-tested-by: Dave Jones <davej@xxxxxxxxxx>
    Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
    Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
    Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>

diff --git a/include/linux/tick.h b/include/linux/tick.h
index 0590523..9a82c7d 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -183,13 +183,8 @@ static inline bool tick_nohz_full_cpu(int cpu)
 
 extern void tick_nohz_init(void);
 extern void __tick_nohz_full_check(void);
+extern void tick_nohz_full_kick(void);
 extern void tick_nohz_full_kick_cpu(int cpu);
-
-static inline void tick_nohz_full_kick(void)
-{
-	tick_nohz_full_kick_cpu(smp_processor_id());
-}
-
 extern void tick_nohz_full_kick_all(void);
 extern void __tick_nohz_task_switch(struct task_struct *tsk);
 #else
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 99aa6ee..f654a8a 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -225,6 +225,20 @@ static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
 };
 
 /*
+ * Kick this CPU if it's full dynticks in order to force it to
+ * re-evaluate its dependency on the tick and restart it if necessary.
+ * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(),
+ * is NMI safe.
+ */
+void tick_nohz_full_kick(void)
+{
+	if (!tick_nohz_full_cpu(smp_processor_id()))
+		return;
+
+	irq_work_queue(&__get_cpu_var(nohz_full_kick_work));
+}
+
+/*
  * Kick the CPU if it's full dynticks in order to force it to
  * re-evaluate its dependency on the tick and restart it if necessary.
  */
--
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