Commit c3466952 authored Dec 03, 2019 by Johannes Weiner Committed by Peter Zijlstra Dec 17, 2019

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

parent 3dfbe25c

kernel/sched/psi.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -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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