From: Wen Yang <wenyang@xxxxxxxxxxxxxxxxx> Subject: mm/page-writeback.c: use div64_ul() for u64-by-unsigned-long divide The two variables 'numerator' and 'denominator', though they are declared as long, they should actually be unsigned long (according to the implementation of the fprop_fraction_percpu() function) And do_div() does a 64-by-32 division, while the divisor 'denominator' is unsigned long, thus 64-bit on 64-bit platforms. Hence the proper function to call is div64_ul(). Link: http://lkml.kernel.org/r/20200102081442.8273-3-wenyang@xxxxxxxxxxxxxxxxx Signed-off-by: Wen Yang <wenyang@xxxxxxxxxxxxxxxxx> Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Qian Cai <cai@xxxxxx> Cc: Tejun Heo <tj@xxxxxxxxxx> Cc: Jens Axboe <axboe@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/page-writeback.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/mm/page-writeback.c~mm-page-writebackc-use-div64_ul-for-u64-by-unsigned-long-divide +++ a/mm/page-writeback.c @@ -766,7 +766,7 @@ static unsigned long __wb_calc_thresh(st struct wb_domain *dom = dtc_dom(dtc); unsigned long thresh = dtc->thresh; u64 wb_thresh; - long numerator, denominator; + unsigned long numerator, denominator; unsigned long wb_min_ratio, wb_max_ratio; /* @@ -777,7 +777,7 @@ static unsigned long __wb_calc_thresh(st wb_thresh = (thresh * (100 - bdi_min_ratio)) / 100; wb_thresh *= numerator; - do_div(wb_thresh, denominator); + wb_thresh = div64_ul(wb_thresh, denominator); wb_min_max_ratio(dtc->wb, &wb_min_ratio, &wb_max_ratio); _
