Perform grant table page allocation outside of the table mutex

witness(4) has found that km_alloc will trigger an rw_enter via uvm_map
and vm_map_lock.  While rw_enter is called with RW_SLEEPFAIL, there's
also an msleep in there, so it's easier to avoid getting in the middle
of that.

diff --git a/sys/dev/pv/xen.c b/sys/dev/pv/xen.c
index 9a469ae..96795da 100644 (file)
--- a/sys/dev/pv/xen.c
+++ b/sys/dev/pv/xen.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: xen.c,v 1.81 2017/03/19 16:55:31 mikeb Exp $  */
+/*     $OpenBSD: xen.c,v 1.82 2017/06/02 20:25:50 mikeb Exp $  */
 
 /*
  * Copyright (c) 2015, 2016, 2017 Mike Belopuhov
@@ -988,6 +988,7 @@ xen_grant_table_grow(struct xen_softc *sc)
 {
        struct xen_add_to_physmap xatp;
        struct xen_gntent *ge;
+       void *va;
        paddr_t pa;
 
        if (sc->sc_gntcnt == sc->sc_gntmax) {
@@ -996,21 +997,21 @@ xen_grant_table_grow(struct xen_softc *sc)
                return (NULL);
        }
 
-       mtx_enter(&sc->sc_gntlck);
-
-       ge = &sc->sc_gnt[sc->sc_gntcnt];
-       ge->ge_table = km_alloc(PAGE_SIZE, &kv_any, &kp_zero, &kd_nowait);
-       if (ge->ge_table == NULL) {
-               mtx_leave(&sc->sc_gntlck);
+       va = km_alloc(PAGE_SIZE, &kv_any, &kp_zero, &kd_nowait);
+       if (va == NULL)
                return (NULL);
-       }
-       if (!pmap_extract(pmap_kernel(), (vaddr_t)ge->ge_table, &pa)) {
+       if (!pmap_extract(pmap_kernel(), (vaddr_t)va, &pa)) {
                printf("%s: grant table page PA extraction failed\n",
                    sc->sc_dev.dv_xname);
-               km_free(ge->ge_table, PAGE_SIZE, &kv_any, &kp_zero);
-               mtx_leave(&sc->sc_gntlck);
+               km_free(va, PAGE_SIZE, &kv_any, &kp_zero);
                return (NULL);
        }
+
+       mtx_enter(&sc->sc_gntlck);
+
+       ge = &sc->sc_gnt[sc->sc_gntcnt];
+       ge->ge_table = va;
+
        xatp.domid = DOMID_SELF;
        xatp.idx = sc->sc_gntcnt;
        xatp.space = XENMAPSPACE_grant_table;