* vm/vm_map.c (_vm_map_entry_create): Temporarily set the current thread
as VM privileged.
---
vm/vm_map.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff --git a/vm/vm_map.c b/vm/vm_map.c
index 4490878..5d544c4 100644
--- a/vm/vm_map.c
+++ b/vm/vm_map.c
@@ -240,8 +240,26 @@ vm_map_entry_t _vm_map_entry_create(map_header)
const struct vm_map_header *map_header;
{
vm_map_entry_t entry;
+ boolean_t vm_privilege;
+ /*
+ * XXX Map entry creation may occur while a map is locked,
+ * for example when clipping entries. If the system is running
+ * low on memory, allocating an entry may block until pages
+ * are available. But if a map used by the default pager is
+ * kept locked, a deadlock occurs.
+ *
+ * This workaround temporarily elevates the current thread
+ * VM privileges to avoid that particular deadlock, and does
+ * so regardless of the map for convenience, and because it's
+ * currently impossible to predict which map the default pager
+ * may depend on.
+ */
+ vm_privilege = current_thread()->vm_privilege;
+ current_thread()->vm_privilege = TRUE;
entry = (vm_map_entry_t) kmem_cache_alloc(&vm_map_entry_cache);
+ current_thread()->vm_privilege = vm_privilege;
+
if (entry == VM_MAP_ENTRY_NULL)
panic("vm_map_entry_create");
--
2.6.4
