- Add a new object flag "OBJ_NEEDSGIANT". We set this flag if the

   underlying vnode requires Giant.
 - In vm_fault only acquire Giant if the underlying object has NEEDSGIANT
   set.
 - In vm_object_shadow inherit the NEEDSGIANT flag from the backing object.

4 files changed, 14 insertions, 4 deletions

diff --git a/sys/vm/vm_fault.c b/sys/vm/vm_fault.c
index 2fc6a0e..0ef7212 100644
--- a/sys/vm/vm_fault.c
+++ b/sys/vm/vm_fault.c
@@ -290,14 +290,17 @@ RetryFault:;
 	 *
 	 * XXX vnode_pager_lock() can block without releasing the map lock.
 	 */
-	if (!fs.map->system_map)
+	if (fs.first_object->flags & OBJ_NEEDGIANT)
 		mtx_lock(&Giant);
 	VM_OBJECT_LOCK(fs.first_object);
 	vm_object_reference_locked(fs.first_object);
 	fs.vp = vnode_pager_lock(fs.first_object);
 	KASSERT(fs.vp == NULL || !fs.map->system_map,
 	    ("vm_fault: vnode-backed object mapped by system map"));
-	if (debug_mpsafevm && !fs.map->system_map)
+	KASSERT((fs.first_object->flags & OBJ_NEEDGIANT) == 0 ||
+	    !fs.map->system_map,
+	    ("vm_fault: Object requiring giant mapped by system map"));
+	if (fs.first_object->flags & OBJ_NEEDGIANT && debug_mpsafevm)
 		mtx_unlock(&Giant);
 	vm_object_pip_add(fs.first_object, 1);
 
@@ -378,10 +381,12 @@ RetryFault:;
 				}
 				unlock_map(&fs);
 				if (fs.vp != NULL) {
-					mtx_lock(&Giant);
+					int vfslck;
+
+					vfslck = VFS_LOCK_GIANT(fs.vp->v_mount);
 					vput(fs.vp);
-					mtx_unlock(&Giant);
 					fs.vp = NULL;
+					VFS_UNLOCK_GIANT(vfslck);
 				}
 				VM_OBJECT_LOCK(fs.object);
 				if (fs.m == vm_page_lookup(fs.object,
diff --git a/sys/vm/vm_object.c b/sys/vm/vm_object.c
index ae01976..63078ff 100644
--- a/sys/vm/vm_object.c
+++ b/sys/vm/vm_object.c
@@ -1230,6 +1230,7 @@ vm_object_shadow(
 			length = PQ_L2_SIZE / 3 + PQ_PRIME1;
 		result->pg_color = (source->pg_color +
 		    length * source->generation) & PQ_L2_MASK;
+		result->flags |= source->flags & OBJ_NEEDGIANT;
 		VM_OBJECT_UNLOCK(source);
 		next_index = (result->pg_color + PQ_L2_SIZE / 3 + PQ_PRIME1) &
 		    PQ_L2_MASK;
diff --git a/sys/vm/vm_object.h b/sys/vm/vm_object.h
index df3bddd..2de9909 100644
--- a/sys/vm/vm_object.h
+++ b/sys/vm/vm_object.h
@@ -145,6 +145,7 @@ struct vm_object {
 #define OBJ_CLEANING	0x0200
 #define	OBJ_ONEMAPPING	0x2000		/* One USE (a single, non-forked) mapping flag */
 #define	OBJ_DISCONNECTWNT 0x4000	/* disconnect from vnode wanted */
+#define	OBJ_NEEDGIANT	0x8000		/* object requires Giant */
 
 #define IDX_TO_OFF(idx) (((vm_ooffset_t)(idx)) << PAGE_SHIFT)
 #define OFF_TO_IDX(off) ((vm_pindex_t)(((vm_ooffset_t)(off)) >> PAGE_SHIFT))
diff --git a/sys/vm/vnode_pager.c b/sys/vm/vnode_pager.c
index 2ad9d15..733eea4 100644
--- a/sys/vm/vnode_pager.c
+++ b/sys/vm/vnode_pager.c
@@ -231,6 +231,8 @@ vnode_pager_alloc(void *handle, vm_ooffset_t size, vm_prot_t prot,
 		object->un_pager.vnp.vnp_size = size;
 
 		object->handle = handle;
+		if (VFS_NEEDSGIANT(vp->v_mount))
+			vm_object_set_flag(object, OBJ_NEEDGIANT);
 		vp->v_object = object;
 	} else {
 		object->ref_count++;
@@ -1188,6 +1190,7 @@ vnode_pager_lock(vm_object_t first_object)
 		VM_OBJECT_UNLOCK(object);
 		if (first_object != object)
 			VM_OBJECT_UNLOCK(first_object);
+		VFS_ASSERT_GIANT(vp->v_mount);
 		if (vget(vp, LK_CANRECURSE | LK_INTERLOCK |
 		    LK_RETRY | LK_SHARED, curthread)) {
 			VM_OBJECT_LOCK(first_object);