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mm/page-writeback: avoid 32-bit overflow in dirty threshold shares #2945

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mm/page-writeback: avoid 32-bit overflow in dirty threshold shares #2945

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8 changes: 5 additions & 3 deletions mm/page-writeback.c
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Original file line number Diff line number Diff line change
Expand Up @@ -883,6 +883,7 @@ static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc,
{
struct wb_domain *dom = dtc_dom(dtc);
struct bdi_writeback *wb = dtc->wb;
u64 threshold = thresh;
u64 wb_thresh;
u64 wb_max_thresh;
unsigned long numerator, denominator;
Expand All @@ -894,13 +895,14 @@ static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc,
fprop_fraction_percpu(&dom->completions, dtc->wb_completions,
&numerator, &denominator);

wb_thresh = (thresh * (100 * BDI_RATIO_SCALE - bdi_min_ratio)) / (100 * BDI_RATIO_SCALE);
wb_thresh = div_u64(threshold * (100 * BDI_RATIO_SCALE - bdi_min_ratio),
100 * BDI_RATIO_SCALE);
wb_thresh *= numerator;
wb_thresh = div64_ul(wb_thresh, denominator);

wb_min_max_ratio(wb, &wb_min_ratio, &wb_max_ratio);

wb_thresh += (thresh * wb_min_ratio) / (100 * BDI_RATIO_SCALE);
wb_thresh += div_u64(threshold * wb_min_ratio, 100 * BDI_RATIO_SCALE);

/*
* It's very possible that wb_thresh is close to 0 not because the
Expand All @@ -916,7 +918,7 @@ static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc,
wb_thresh = max(wb_thresh, (thresh - dtc->dirty) / 8);
}

wb_max_thresh = thresh * wb_max_ratio / (100 * BDI_RATIO_SCALE);
wb_max_thresh = div_u64(threshold * wb_max_ratio, 100 * BDI_RATIO_SCALE);
if (wb_thresh > wb_max_thresh)
wb_thresh = wb_max_thresh;

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