Commit b0ab99e7 authored Jun 14, 2014 by Mateusz Guzik Committed by Ingo Molnar Jul 16, 2014

sched: Fix possible divide by zero in avg_atom() calculation



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
division.

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 <mguzik@redhat.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1402750809-31991-1-git-send-email-mguzik@redhat.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent b6220ad6

kernel/sched/debug.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -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);
		else
		avg_atom = -1LL;