[POWERPC] Fix possible division by zero in scaled time accounting

If we get no user time and no system time allocated since the last
account_system_vtime, the system to user time ratio estimate can end
up dividing by zero.

This was causing a problem noticed by Balbir Singh.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index c0d77723ba11..a925a8eae121 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -241,8 +241,9 @@ void account_system_vtime(struct task_struct *tsk)
                 /* deltascaled includes both user and system time.
                  * Hence scale it based on the purr ratio to estimate
                  * the system time */
-                deltascaled = deltascaled * get_paca()->system_time /
-                        (get_paca()->system_time + get_paca()->user_time);
+                if (get_paca()->user_time)
+                        deltascaled = deltascaled * get_paca()->system_time /
+                             (get_paca()->system_time + get_paca()->user_time);
                 delta += get_paca()->system_time;
                 get_paca()->system_time = 0;
         }