EN-16:17: virtual memory issues.

Due to increased parallelism and optimizations in several parts of the
system, the previously latent bugs in VM become much easier to trigger,
affecting a significant number of the FreeBSD users.  The exact technical
details of the issues are provided in the commit messages of the merged
revisions, which are listed below with short summaries.

r301184 prevent parallel object collapses, fixes object lifecycle
r301436 do not leak the vm object lock, fixes overcommit disable
r302243 avoid the active object marking for vm.vmtotal sysctl, fixes
        "vodead" hangs
r302513 vm_fault() race with the vm_object_collapse(), fixes spurious
        SIGSEGV
r303291 postpone BO_DEAD, fixes panic on fast vnode reclaim

Approved by:	so

5 files changed, 65 insertions, 51 deletions

diff --git a/sys/kern/vfs_subr.c b/sys/kern/vfs_subr.c
index aa81313..85af62e 100644
--- a/sys/kern/vfs_subr.c
+++ b/sys/kern/vfs_subr.c
@@ -2934,7 +2934,13 @@ vgonel(struct vnode *vp)
 	    TAILQ_EMPTY(&vp->v_bufobj.bo_clean.bv_hd) &&
 	    vp->v_bufobj.bo_clean.bv_cnt == 0,
 	    ("vp %p bufobj not invalidated", vp));
-	vp->v_bufobj.bo_flag |= BO_DEAD;
+
+	/*
+	 * For VMIO bufobj, BO_DEAD is set in vm_object_terminate()
+	 * after the object's page queue is flushed.
+	 */
+	if (vp->v_bufobj.bo_object == NULL)
+		vp->v_bufobj.bo_flag |= BO_DEAD;
 	BO_UNLOCK(&vp->v_bufobj);
 
 	/*
diff --git a/sys/vm/vm_fault.c b/sys/vm/vm_fault.c
index b5ac58f..d65cda2 100644
--- a/sys/vm/vm_fault.c
+++ b/sys/vm/vm_fault.c
@@ -286,7 +286,7 @@ vm_fault_hold(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
 	vm_prot_t prot;
 	long ahead, behind;
 	int alloc_req, era, faultcount, nera, reqpage, result;
-	boolean_t growstack, is_first_object_locked, wired;
+	boolean_t dead, growstack, is_first_object_locked, wired;
 	int map_generation;
 	vm_object_t next_object;
 	vm_page_t marray[VM_FAULT_READ_MAX];
@@ -423,11 +423,18 @@ fast_failed:
 	fs.pindex = fs.first_pindex;
 	while (TRUE) {
 		/*
-		 * If the object is dead, we stop here
+		 * If the object is marked for imminent termination,
+		 * we retry here, since the collapse pass has raced
+		 * with us.  Otherwise, if we see terminally dead
+		 * object, return fail.
 		 */
-		if (fs.object->flags & OBJ_DEAD) {
+		if ((fs.object->flags & OBJ_DEAD) != 0) {
+			dead = fs.object->type == OBJT_DEAD;
 			unlock_and_deallocate(&fs);
-			return (KERN_PROTECTION_FAILURE);
+			if (dead)
+				return (KERN_PROTECTION_FAILURE);
+			pause("vmf_de", 1);
+			goto RetryFault;
 		}
 
 		/*
diff --git a/sys/vm/vm_meter.c b/sys/vm/vm_meter.c
index 75974c6..3f8ba38 100644
--- a/sys/vm/vm_meter.c
+++ b/sys/vm/vm_meter.c
@@ -93,29 +93,31 @@ SYSCTL_PROC(_vm, VM_LOADAVG, loadavg, CTLTYPE_STRUCT | CTLFLAG_RD |
     CTLFLAG_MPSAFE, NULL, 0, sysctl_vm_loadavg, "S,loadavg",
     "Machine loadaverage history");
 
+/*
+ * This function aims to determine if the object is mapped,
+ * specifically, if it is referenced by a vm_map_entry.  Because
+ * objects occasionally acquire transient references that do not
+ * represent a mapping, the method used here is inexact.  However, it
+ * has very low overhead and is good enough for the advisory
+ * vm.vmtotal sysctl.
+ */
+static bool
+is_object_active(vm_object_t obj)
+{
+
+	return (obj->ref_count > obj->shadow_count);
+}
+
 static int
 vmtotal(SYSCTL_HANDLER_ARGS)
 {
-	struct proc *p;
 	struct vmtotal total;
-	vm_map_entry_t entry;
 	vm_object_t object;
-	vm_map_t map;
-	int paging;
+	struct proc *p;
 	struct thread *td;
-	struct vmspace *vm;
 
 	bzero(&total, sizeof(total));
-	/*
-	 * Mark all objects as inactive.
-	 */
-	mtx_lock(&vm_object_list_mtx);
-	TAILQ_FOREACH(object, &vm_object_list, object_list) {
-		VM_OBJECT_WLOCK(object);
-		vm_object_clear_flag(object, OBJ_ACTIVE);
-		VM_OBJECT_WUNLOCK(object);
-	}
-	mtx_unlock(&vm_object_list_mtx);
+
 	/*
 	 * Calculate process statistics.
 	 */
@@ -136,11 +138,15 @@ vmtotal(SYSCTL_HANDLER_ARGS)
 				case TDS_INHIBITED:
 					if (TD_IS_SWAPPED(td))
 						total.t_sw++;
-					else if (TD_IS_SLEEPING(td) &&
-					    td->td_priority <= PZERO)
-						total.t_dw++;
-					else
-						total.t_sl++;
+					else if (TD_IS_SLEEPING(td)) {
+						if (td->td_priority <= PZERO)
+							total.t_dw++;
+						else
+							total.t_sl++;
+						if (td->td_wchan ==
+						    &cnt.v_free_count)
+							total.t_pw++;
+					}
 					break;
 
 				case TDS_CAN_RUN:
@@ -158,29 +164,6 @@ vmtotal(SYSCTL_HANDLER_ARGS)
 			}
 		}
 		PROC_UNLOCK(p);
-		/*
-		 * Note active objects.
-		 */
-		paging = 0;
-		vm = vmspace_acquire_ref(p);
-		if (vm == NULL)
-			continue;
-		map = &vm->vm_map;
-		vm_map_lock_read(map);
-		for (entry = map->header.next;
-		    entry != &map->header; entry = entry->next) {
-			if ((entry->eflags & MAP_ENTRY_IS_SUB_MAP) ||
-			    (object = entry->object.vm_object) == NULL)
-				continue;
-			VM_OBJECT_WLOCK(object);
-			vm_object_set_flag(object, OBJ_ACTIVE);
-			paging |= object->paging_in_progress;
-			VM_OBJECT_WUNLOCK(object);
-		}
-		vm_map_unlock_read(map);
-		vmspace_free(vm);
-		if (paging)
-			total.t_pw++;
 	}
 	sx_sunlock(&allproc_lock);
 	/*
@@ -206,9 +189,18 @@ vmtotal(SYSCTL_HANDLER_ARGS)
 			 */
 			continue;
 		}
+		if (object->ref_count == 1 &&
+		    (object->flags & OBJ_NOSPLIT) != 0) {
+			/*
+			 * Also skip otherwise unreferenced swap
+			 * objects backing tmpfs vnodes, and POSIX or
+			 * SysV shared memory.
+			 */
+			continue;
+		}
 		total.t_vm += object->size;
 		total.t_rm += object->resident_page_count;
-		if (object->flags & OBJ_ACTIVE) {
+		if (is_object_active(object)) {
 			total.t_avm += object->size;
 			total.t_arm += object->resident_page_count;
 		}
@@ -216,7 +208,7 @@ vmtotal(SYSCTL_HANDLER_ARGS)
 			/* shared object */
 			total.t_vmshr += object->size;
 			total.t_rmshr += object->resident_page_count;
-			if (object->flags & OBJ_ACTIVE) {
+			if (is_object_active(object)) {
 				total.t_avmshr += object->size;
 				total.t_armshr += object->resident_page_count;
 			}
diff --git a/sys/vm/vm_object.c b/sys/vm/vm_object.c
index e9d1280..847056f 100644
--- a/sys/vm/vm_object.c
+++ b/sys/vm/vm_object.c
@@ -737,6 +737,10 @@ vm_object_terminate(vm_object_t object)
 
 		vinvalbuf(vp, V_SAVE, 0, 0);
 
+		BO_LOCK(&vp->v_bufobj);
+		vp->v_bufobj.bo_flag |= BO_DEAD;
+		BO_UNLOCK(&vp->v_bufobj);
+
 		VM_OBJECT_WLOCK(object);
 	}
 
@@ -1722,6 +1726,9 @@ vm_object_collapse(vm_object_t object)
 		 * case.
 		 */
 		if (backing_object->ref_count == 1) {
+			vm_object_pip_add(object, 1);
+			vm_object_pip_add(backing_object, 1);
+
 			/*
 			 * If there is exactly one reference to the backing
 			 * object, we can collapse it into the parent.  
@@ -1793,11 +1800,13 @@ vm_object_collapse(vm_object_t object)
 			KASSERT(backing_object->ref_count == 1, (
 "backing_object %p was somehow re-referenced during collapse!",
 			    backing_object));
+			vm_object_pip_wakeup(backing_object);
 			backing_object->type = OBJT_DEAD;
 			backing_object->ref_count = 0;
 			VM_OBJECT_WUNLOCK(backing_object);
 			vm_object_destroy(backing_object);
 
+			vm_object_pip_wakeup(object);
 			object_collapses++;
 		} else {
 			vm_object_t new_backing_object;
@@ -2130,6 +2139,7 @@ vm_object_coalesce(vm_object_t prev_object, vm_ooffset_t prev_offset,
 		 */
 		if (!reserved && !swap_reserve_by_cred(ptoa(next_size),
 		    prev_object->cred)) {
+			VM_OBJECT_WUNLOCK(prev_object);
 			return (FALSE);
 		}
 		prev_object->charge += ptoa(next_size);
diff --git a/sys/vm/vm_object.h b/sys/vm/vm_object.h
index ac8feae..f45aa9e 100644
--- a/sys/vm/vm_object.h
+++ b/sys/vm/vm_object.h
@@ -181,7 +181,6 @@ struct vm_object {
  */
 #define	OBJ_FICTITIOUS	0x0001		/* (c) contains fictitious pages */
 #define	OBJ_UNMANAGED	0x0002		/* (c) contains unmanaged pages */
-#define OBJ_ACTIVE	0x0004		/* active objects */
 #define OBJ_DEAD	0x0008		/* dead objects (during rundown) */
 #define	OBJ_NOSPLIT	0x0010		/* dont split this object */
 #define OBJ_PIPWNT	0x0040		/* paging in progress wanted */