> -----Original Message----- > From: Rik van Riel [mailto:riel@xxxxxxxxxx] > Sent: Tuesday, April 29, 2014 3:19 PM > To: linux-kernel@xxxxxxxxxxxxxxx > Cc: linux-mm@xxxxxxxxx; sandeen@xxxxxxxxxx; akpm@xxxxxxxxxxxxxxxxxxxx; jweiner@xxxxxxxxxx; Motohiro Kosaki JP; > mhocko@xxxxxxx; fengguang.wu@xxxxxxxxx; mpatlasov@xxxxxxxxxxxxx > Subject: [PATCH] mm,writeback: fix divide by zero in pos_ratio_polynom > > It is possible for "limit - setpoint + 1" to equal zero, leading to a divide by zero error. Blindly adding 1 to "limit - setpoint" is not working, > so we need to actually test the divisor before calling div64. > > Signed-off-by: Rik van Riel <riel@xxxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx Fairly obvious fix. Acked-by: KOSAKI Motohiro <Kosaki.motohiro@xxxxxxxxxxxxxx> > --- > mm/page-writeback.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/mm/page-writeback.c b/mm/page-writeback.c index ef41349..2682516 100644 > --- a/mm/page-writeback.c > +++ b/mm/page-writeback.c > @@ -597,11 +597,16 @@ static inline long long pos_ratio_polynom(unsigned long setpoint, > unsigned long dirty, > unsigned long limit) > { > + unsigned int divisor; > long long pos_ratio; > long x; > > + divisor = limit - setpoint; > + if (!divisor) > + divisor = 1; > + > x = div_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT, > - limit - setpoint + 1); > + divisor); > pos_ratio = x; > pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; > pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href