untrusted comment: signature from openbsd 5.8 base secret key
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OpenBSD 5.8 errata 3, Sep 28, 2015:

An incorrect operation in uvm could result in system panics.

Apply by doing:
   signify -Vep /etc/signify/openbsd-58-base.pub -x 003_uvm.patch.sig \
       -m - | (cd /usr/src && patch -p0)

And then rebuild and install a kernel:
   cd /usr/src/sys/arch/`machine`/conf
   KK=`sysctl -n kern.osversion | cut -d# -f1`
   config $KK
   cd ../compile/$KK
   make
   make install


Index: sys/uvm/uvm_km.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_km.c,v
retrieving revision 1.126
diff -u -p -r1.126 uvm_km.c
--- sys/uvm/uvm_km.c    7 Feb 2015 08:21:24 -0000       1.126
+++ sys/uvm/uvm_km.c    28 Sep 2015 18:07:40 -0000
@@ -259,7 +259,6 @@ uvm_km_pgremove(struct uvm_object *uobj,
               slot = uao_dropswap(uobj, curoff >> PAGE_SHIFT);

               if (pp != NULL) {
-                       atomic_clearbits_int(&pp->pg_flags, PQ_AOBJ);
                       uvm_lock_pageq();
                       uvm_pagefree(pp);
                       uvm_unlock_pageq();