D36084.diff
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	diff --git a/sys/vm/vm_page.c b/sys/vm/vm_page.c
	--- a/sys/vm/vm_page.c
	+++ b/sys/vm/vm_page.c
	@@ -973,27 +973,13 @@
	{
	u_int x;

	- vm_page_assert_sbusied(m);
	-
	- x = vm_page_busy_fetch(m);
	- for (;;) {
	- KASSERT(x != VPB_FREED,
	- ("vm_page_sunbusy: Unlocking freed page."));
	- if (VPB_SHARERS(x) > 1) {
	- if (atomic_fcmpset_int(&m->busy_lock, &x,
	- x - VPB_ONE_SHARER))
	- break;
	- continue;
	- }
	- KASSERT((x & ~VPB_BIT_WAITERS) == VPB_SHARERS_WORD(1),
	- ("vm_page_sunbusy: invalid lock state"));
	- if (!atomic_fcmpset_rel_int(&m->busy_lock, &x, VPB_UNBUSIED))
	- continue;
	- if ((x & VPB_BIT_WAITERS) == 0)
	- break;
	+ atomic_thread_fence_rel();
	+ x = atomic_fetchadd_int(&m->busy_lock, -VPB_ONE_SHARER);
	+ KASSERT(x != VPB_FREED, ("page %p is freed", m));
	+ KASSERT(x != VPB_UNBUSIED && (x & VPB_BIT_SHARED) != 0,
	+ ("page %p not sbusied", m));
	+ if (x == (VPB_SHARERS_WORD(1) \| VPB_BIT_WAITERS))
	wakeup(m);
	- break;
	- }
	}

	/*