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Date:	Fri,  8 Aug 2014 13:39:27 -0700
From:	Kamal Mostafa <>
Cc:	Mateusz Guzik <>,
	Peter Zijlstra <>,
	Linus Torvalds <>,
	Ingo Molnar <>,
	Kamal Mostafa <>
Subject: [PATCH 3.13 144/259] sched: Fix possible divide by zero in avg_atom() calculation -stable review patch.  If anyone has any objections, please let me know.


From: Mateusz Guzik <>

commit b0ab99e7736af88b8ac1b7ae50ea287fffa2badc upstream.

proc_sched_show_task() does:

  if (nr_switches)
	do_div(avg_atom, nr_switches);

nr_switches is unsigned long and do_div truncates it to 32 bits, which
means it can test non-zero on e.g. x86-64 and be truncated to zero for

Fix the problem by using div64_ul() instead.

As a side effect calculations of avg_atom for big nr_switches are now correct.

Signed-off-by: Mateusz Guzik <>
Signed-off-by: Peter Zijlstra <>
Cc: Linus Torvalds <>
Signed-off-by: Ingo Molnar <>
Signed-off-by: Kamal Mostafa <>
 kernel/sched/debug.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 5c34d18..0c60913 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -608,7 +608,7 @@ void proc_sched_show_task(struct task_struct *p, struct seq_file *m)
 		avg_atom = p->se.sum_exec_runtime;
 		if (nr_switches)
-			do_div(avg_atom, nr_switches);
+			avg_atom = div64_ul(avg_atom, nr_switches);
 			avg_atom = -1LL;

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