On Tue, 29 Apr 2014 15:19:10 -0400 Rik van Riel <riel@xxxxxxxxxx> wrote: > 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. > > ... > > --- 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; I'm thinking this would be better as a ulong so I don't have to worry my pretty head over truncation things? > 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; --- a/mm/page-writeback.c~mm-page-writebackc-fix-divide-by-zero-in-pos_ratio_polynom-fix +++ a/mm/page-writeback.c @@ -597,13 +597,13 @@ static inline long long pos_ratio_polyno unsigned long dirty, unsigned long limit) { - unsigned int divisor; + unsigned long divisor; long long pos_ratio; long x; divisor = limit - setpoint; if (!divisor) - divisor = 1; + divisor = 1; /* Avoid div-by-zero */ x = div_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT, divisor); _ -- 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=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>