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Subject[tip: sched/urgent] psi: Fix a division error in psi poll()
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@cmpxchg.org>
AuthorDate: Tue, 03 Dec 2019 13:35:24 -05:00
Committer: Peter Zijlstra <peterz@infradead.org>
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@cmpxchg.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Cc: Jingfeng Xie <xiejingfeng@linux.alibaba.com>
Link: https://lkml.kernel.org/r/20191203183524.41378-3-hannes@cmpxchg.org
---
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;
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