Reimplement and/or implement vnet list locking by replacing a mostly

unused custom mutex/condvar-based sleep locks with two locks: an
rwlock (for non-sleeping use) and sxlock (for sleeping use).  Either
acquired for read is sufficient to stabilize the vnet list, but both
must be acquired for write to modify the list.

Replace previous no-op read locking macros, used in various places
in the stack, with actual locking to prevent race conditions.  Callers
must declare when they may perform unbounded sleeps or not when
selecting how to lock.

Refactor vnet sysinits so that the vnet list and locks are initialized
before kernel modules are linked, as the kernel linker will use them
for modules loaded by the boot loader.

Update various consumers of these KPIs based on whether they may sleep
or not.

Reviewed by:	bz
Approved by:	re (kib)

1 files changed, 27 insertions, 21 deletions

diff --git a/sys/kern/kern_vimage.c b/sys/kern/kern_vimage.c
index 328b2ba..f3d4a86 100644
--- a/sys/kern/kern_vimage.c
+++ b/sys/kern/kern_vimage.c
@@ -58,23 +58,22 @@ static void vnet_mod_complete_registration(struct vnet_modlink *);
 static int vnet_mod_constructor(struct vnet_modlink *);
 static int vnet_mod_destructor(struct vnet_modlink *);
 
-#define	VNET_LIST_WLOCK()						\
-	mtx_lock(&vnet_list_refc_mtx);					\
-	while (vnet_list_refc != 0)					\
-		cv_wait(&vnet_list_condvar, &vnet_list_refc_mtx);
+struct rwlock		vnet_rwlock;
+struct sx		vnet_sxlock;
 
-#define	VNET_LIST_WUNLOCK()						\
-	mtx_unlock(&vnet_list_refc_mtx);
+#define	VNET_LIST_WLOCK() do {						\
+	sx_xlock(&vnet_sxlock);						\
+	rw_wlock(&vnet_rwlock);						\
+} while (0)
 
-struct vnet_list_head vnet_head;
-
-struct cv vnet_list_condvar;
-struct mtx vnet_list_refc_mtx;
-int vnet_list_refc = 0;
+#define	VNET_LIST_WUNLOCK() do {					\
+	rw_wunlock(&vnet_rwlock);					\
+	sx_xunlock(&vnet_sxlock);					\
+} while (0)
 
+struct vnet_list_head vnet_head;
 struct vnet *vnet0;
 
-
 /*
  * Move an ifnet to or from another vnet, specified by the jail id.
  */
@@ -373,16 +372,22 @@ vnet_foreach(void (*vnet_foreach_fn)(struct vnet *, void *), void *arg)
 }
 
 static void
-vi_init(void *unused)
+vnet_init_prelink(void *arg)
 {
 
-	TAILQ_INIT(&vnet_modlink_head);
-	TAILQ_INIT(&vnet_modpending_head);
-
+	rw_init(&vnet_rwlock, "vnet_rwlock");
+	sx_init(&vnet_sxlock, "vnet_sxlock");
 	LIST_INIT(&vnet_head);
+}
+SYSINIT(vnet_init_prelink, SI_SUB_VNET_PRELINK, SI_ORDER_FIRST,
+    vnet_init_prelink, NULL);
+
+static void
+vnet0_init(void *arg)
+{
 
-	mtx_init(&vnet_list_refc_mtx, "vnet_list_refc_mtx", NULL, MTX_DEF);
-	cv_init(&vnet_list_condvar, "vnet_list_condvar");
+	TAILQ_INIT(&vnet_modlink_head);
+	TAILQ_INIT(&vnet_modpending_head);
 
 	/*
 	 * We MUST clear curvnet in vi_init_done() before going SMP,
@@ -391,9 +396,10 @@ vi_init(void *unused)
 	 */
 	curvnet = prison0.pr_vnet = vnet0 = vnet_alloc();
 }
+SYSINIT(vnet0_init, SI_SUB_VNET, SI_ORDER_FIRST, vnet0_init, NULL);
 
 static void
-vi_init_done(void *unused)
+vnet_init_done(void *unused)
 {
 	struct vnet_modlink *vml_iter;
 
@@ -411,8 +417,8 @@ vi_init_done(void *unused)
 	panic("going nowhere without my vnet modules!");
 }
 
-SYSINIT(vimage, SI_SUB_VIMAGE, SI_ORDER_FIRST, vi_init, NULL);
-SYSINIT(vimage_done, SI_SUB_VIMAGE_DONE, SI_ORDER_FIRST, vi_init_done, NULL);
+SYSINIT(vnet_init_done, SI_SUB_VNET_DONE, SI_ORDER_FIRST, vnet_init_done,
+    NULL);
 
 #ifdef DDB
 DB_SHOW_COMMAND(vnets, db_show_vnets)