[PATCH 21/32] nohz/cpuset: Flush cputime on threads in nohz cpusets when waiting leader

[Frederic Weisbecker <fweisbec@gmail.com>]

When we wait for a zombie task, flush the cputimes on nohz cpusets
in case we are waiting for a group leader that has threads running
in nohz CPUs. This way thread_group_times() doesn't report stale
values.

<doubts>
If I understood well the code, by the time we call that thread_group_times(),
we may have childs that are still running, so this is necessary.
But I need to check deeper.
</doubts>

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Alessio Igor Bogani <abogani@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Avi Kivity <avi@redhat.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Max Krasnyansky <maxk@qualcomm.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Zen Lin <zen@openhuawei.org>
---
 kernel/exit.c |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 4b4042f..c194662 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -52,6 +52,7 @@
 #include <linux/hw_breakpoint.h>
 #include <linux/oom.h>
 #include <linux/writeback.h>
+#include <linux/cpuset.h>
 
 #include <asm/uaccess.h>
 #include <asm/unistd.h>
@@ -1712,6 +1713,13 @@ repeat:
 	   (!wo->wo_pid || hlist_empty(&wo->wo_pid->tasks[wo->wo_type])))
 		goto notask;
 
+	/*
+	 * For cputime in sub-threads before adding them.
+	 * Must be called outside tasklist_lock lock because write lock
+	 * can be acquired under irqs disabled.
+	 */
+	cpuset_nohz_flush_cputimes();
+
 	set_current_state(TASK_INTERRUPTIBLE);
 	read_lock(&tasklist_lock);
 	tsk = current;
-- 
1.7.5.4