kernel - Acquire vm_token in pmap_remove_all() (2)

* Remove this, the token is already acquired in all pmap_remove_all()
  paths.

* Instead, try catching the problem in pmap_remove_all(m) by re-validating
  the pv_entry (essentially detecting a removal race).

diff --git a/sys/platform/pc32/i386/pmap.c b/sys/platform/pc32/i386/pmap.c
index 207153b..2b91cf0 100644 (file)
--- a/sys/platform/pc32/i386/pmap.c
+++ b/sys/platform/pc32/i386/pmap.c
@@ -1513,6 +1513,7 @@ pmap_release(struct pmap *pmap)
        spin_unlock(&pmap_spin);
 
        vm_object_hold(object);
+       /*lwkt_gettoken(&vm_token);*/
        do {
                info.error = 0;
                info.mpte = NULL;
@@ -1525,6 +1526,7 @@ pmap_release(struct pmap *pmap)
                                info.error = 1;
                }
        } while (info.error);
+       /*lwkt_reltoken(&vm_token);*/
        vm_object_drop(object);
 
        pmap->pm_cached = 0;
@@ -2056,13 +2058,21 @@ pmap_remove_all(vm_page_t m)
        if (TAILQ_EMPTY(&m->md.pv_list))
                return;
 
-       lwkt_gettoken(&vm_token);
        pmap_inval_init(&info);
        while ((pv = TAILQ_FIRST(&m->md.pv_list)) != NULL) {
                pmap = pv->pv_pmap;
                KKASSERT(pmap->pm_stats.resident_count > 0);
                --pmap->pm_stats.resident_count;
                pmap_hold(pmap);
+               vm_object_hold(pmap->pm_pteobj);
+
+               if (pv != TAILQ_FIRST(&m->md.pv_list)) {
+                       kprintf("pmap_remove_all: %p pv %p went away\n",
+                               pmap, pv);
+                       vm_object_drop(pmap->pm_pteobj);
+                       pmap_drop(pmap);
+                       continue;
+               }
 
                pte = pmap_pte_quick(pmap, pv->pv_va);
                pmap_inval_interlock(&info, pmap, pv->pv_va);
@@ -2100,7 +2110,6 @@ pmap_remove_all(vm_page_t m)
                        atomic_add_int(&m->object->agg_pv_list_count, -1);
                if (TAILQ_EMPTY(&m->md.pv_list))
                        vm_page_flag_clear(m, PG_MAPPED | PG_WRITEABLE);
-               vm_object_hold(pmap->pm_pteobj);
                pmap_unuse_pt(pmap, pv->pv_va, pv->pv_ptem, &info);
                vm_object_drop(pmap->pm_pteobj);
                free_pv_entry(pv);
@@ -2108,7 +2117,6 @@ pmap_remove_all(vm_page_t m)
        }
        KKASSERT((m->flags & (PG_MAPPED|PG_WRITEABLE)) == 0);
        pmap_inval_done(&info);
-       lwkt_reltoken(&vm_token);
 }
 
 /*