Messages in this thread | | | Date | Tue, 29 Apr 2014 18:48:11 -0400 | From | Rik van Riel <> | Subject | Re: [PATCH] mm,writeback: fix divide by zero in pos_ratio_polynom |
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On 04/29/2014 06:39 PM, Andrew Morton wrote: > On Tue, 29 Apr 2014 15:19:10 -0400 Rik van Riel <riel@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
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