On 04/29/2014 06:39 PM, Andrew Morton wrote: > On Tue, 29 Apr 2014 15:19:10 -0400 Rik van Riel <r...@redhat.com> 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?
I looked at div_*64, and the second argument is a 32 bit variable. I guess a long would be ok, since if we are dividing by more than 4 billion we don't really care :) static inline s64 div_s64(s64 dividend, s32 divisor) > --- > 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 */ Works for me :) -- All rights reversed -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/