linux-kernel - [PATCH 2/2] psi: fix a division error in psi poll()

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Message-Id: <20191203183524.41378-3-hannes@cmpxchg.org>
Date:   Tue,  3 Dec 2019 13:35:24 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Jingfeng Xie <xiejingfeng@...ux.alibaba.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] 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@...xchg.org>
Reviewed-by: Suren Baghdasaryan <surenb@...gle.com>
---
 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 970db4686dd4..ce8f6748678a 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;
-- 
2.24.0