D8195.1793395395.diff
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	Index: head/sys/vm/vm_page.c
	===================================================================
	--- head/sys/vm/vm_page.c
	+++ head/sys/vm/vm_page.c
	@@ -655,15 +655,26 @@
	vm_page_busy_downgrade(vm_page_t m)
	{
	u_int x;
	+ bool locked;

	vm_page_assert_xbusied(m);
	+ locked = mtx_owned(vm_page_lockptr(m));

	for (;;) {
	x = m->busy_lock;
	x &= VPB_BIT_WAITERS;
	+ if (x != 0 && !locked)
	+ vm_page_lock(m);
	if (atomic_cmpset_rel_int(&m->busy_lock,
	- VPB_SINGLE_EXCLUSIVER \| x, VPB_SHARERS_WORD(1) \| x))
	+ VPB_SINGLE_EXCLUSIVER \| x, VPB_SHARERS_WORD(1)))
	break;
	+ if (x != 0 && !locked)
	+ vm_page_unlock(m);
	+ }
	+ if (x != 0) {
	+ wakeup(m);
	+ if (!locked)
	+ vm_page_unlock(m);
	}
	}