[tip: sched/urgent] psi: Fix a division error in psi poll()

[tip-bot2 for Johannes Weiner]

The following commit has been merged into the sched/urgent branch of tip:

Commit-ID:     c3466952ca1514158d7c16c9cfc48c27d5c5dc0f
Gitweb:        https://git.kernel.org/tip/c3466952ca1514158d7c16c9cfc48c27d5c5dc0f
Author:        Johannes Weiner <hannes@xxxxxxxxxxx>
AuthorDate:    Tue, 03 Dec 2019 13:35:24 -05:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Tue, 17 Dec 2019 13:32:48 +01:00

psi: Fix a division error in psi poll()

The psi window size is a u64 an can be up to 10 seconds right now,
which exceeds the lower 32 bits of the variable. We currently use
div_u64 for it, which is meant only for 32-bit divisors. The result is
garbage pressure sampling values and even potential div0 crashes.

Use div64_u64.

Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Jingfeng Xie <xiejingfeng@xxxxxxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20191203183524.41378-3-hannes@xxxxxxxxxxx
---
 kernel/sched/psi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 970db46..ce8f674 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -482,7 +482,7 @@ static u64 window_update(struct psi_window *win, u64 now, u64 value)
 		u32 remaining;
 
 		remaining = win->size - elapsed;
-		growth += div_u64(win->prev_growth * remaining, win->size);
+		growth += div64_u64(win->prev_growth * remaining, win->size);
 	}
 
 	return growth;