[Devel] [PATCH rh7] fs/mm: writeback: fix div/0

[Vladimir Davydov]

https://jira.sw.ru/browse/PSBM-46146

Fixes: d179e86ac429 ("fs/mm: writeback: fix per bdi dirty background threshold calculation")
Signed-off-by: Vladimir Davydov <vdavydov at virtuozzo.com>
---
 fs/fs-writeback.c   | 2 +-
 mm/page-writeback.c | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 55eca543f921..5c9a0828ba18 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -845,7 +845,7 @@ static bool over_bground_thresh(struct backing_dev_info *bdi)
 
 	bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
 	bdi_bg_thresh = div_u64((u64)bdi_thresh * background_thresh,
-				dirty_thresh);
+				dirty_thresh + 1);
 
 	if (bdi_stat(bdi, BDI_RECLAIMABLE) > bdi_bg_thresh)
 		return true;
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 46987e86c5a0..3b881f30dbe5 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -791,7 +791,8 @@ static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
 		if (bdi_dirty >= bdi_thresh)
 			return 0;
 
-		bdi_bg_thresh = div_u64((u64)bdi_thresh * bg_thresh, thresh);
+		bdi_bg_thresh = div_u64((u64)bdi_thresh * bg_thresh,
+					thresh + 1);
 		bdi_setpoint = dirty_freerun_ceiling(bdi_thresh,
 						     bdi_bg_thresh);
 
-- 
2.1.4