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); } }