[src/trunk]: src/sys/kern When deciding to defer in vrelel():

[hannken <hannken%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/9344a8470ab6
branches:  trunk
changeset: 325120:9344a8470ab6
user:      hannken <hannken%NetBSD.org@localhost>
date:      Sat Dec 07 10:03:28 2013 +0000

description:
When deciding to defer in vrelel():
- No need to always defer layer vnodes, if we get the vnode lock it
  is safe to inactivate.
- Always use VOP_LOCK(), it makes no sense to use vn_lock() here.
- No need to drop v_interlock for VOP_LOCK(... LK_NOWAIT).

diffstat:

 sys/kern/vfs_vnode.c |  40 ++++++++++++----------------------------
 1 files changed, 12 insertions(+), 28 deletions(-)

diffs (88 lines):

diff -r 918fdac94f86 -r 9344a8470ab6 sys/kern/vfs_vnode.c
--- a/sys/kern/vfs_vnode.c      Sat Dec 07 09:20:22 2013 +0000
+++ b/sys/kern/vfs_vnode.c      Sat Dec 07 10:03:28 2013 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: vfs_vnode.c,v 1.29 2013/12/01 17:29:40 christos Exp $  */
+/*     $NetBSD: vfs_vnode.c,v 1.30 2013/12/07 10:03:28 hannken Exp $   */
 
 /*-
  * Copyright (c) 1997-2011 The NetBSD Foundation, Inc.
@@ -116,7 +116,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vfs_vnode.c,v 1.29 2013/12/01 17:29:40 christos Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_vnode.c,v 1.30 2013/12/07 10:03:28 hannken Exp $");
 
 #define _VFS_VNODE_PRIVATE
 
@@ -626,27 +626,22 @@
                 * locking is pushed down into the file systems.
                 *
                 * Defer vnode release to vrele_thread if caller
-                * requests it explicitly.
+                * requests it explicitly or is the pagedaemon.
                 */
                if ((curlwp == uvm.pagedaemon_lwp) ||
                    (flags & VRELEL_ASYNC_RELE) != 0) {
-                       /* The pagedaemon can't wait around; defer. */
                        defer = true;
                } else if (curlwp == vrele_lwp) {
                        /*
                         * We have to try harder.
                         */
                        mutex_exit(vp->v_interlock);
-                       error = vn_lock(vp, LK_EXCLUSIVE);
-                       if (error != 0) {
-                               /* XXX */
-                               vnpanic(vp, "%s: unable to lock %p",
-                                   __func__, vp);
-                       }
+                       error = VOP_LOCK(vp, LK_EXCLUSIVE);
+                       KASSERT(error == 0);
                        mutex_enter(vp->v_interlock);
                        /*
-                        * if we did get another reference while
-                        * sleeping, don't try to inactivate it yet.
+                        * If the node got another reference while sleeping,
+                        * don't try to inactivate it yet.
                         */
                        if (__predict_false(vtryrele(vp))) {
                                VOP_UNLOCK(vp);
@@ -659,31 +654,20 @@
                                return;
                        }
                        defer = false;
-               } else if ((vp->v_iflag & VI_LAYER) != 0) {
-                       /* 
-                        * Acquiring the stack's lock in vclean() even
-                        * for an honest vput/vrele is dangerous because
-                        * our caller may hold other vnode locks; defer.
-                        */
-                       defer = true;
                } else {
                        /* If we can't acquire the lock, then defer. */
-                       mutex_exit(vp->v_interlock);
-                       error = vn_lock(vp, LK_EXCLUSIVE | LK_NOWAIT);
-                       if (error != 0) {
-                               defer = true;
-                       } else {
-                               defer = false;
-                       }
-                       mutex_enter(vp->v_interlock);
+                       error = VOP_LOCK(vp, LK_EXCLUSIVE | LK_NOWAIT);
+                       defer = (error != 0);
                }
 
+               KASSERT(mutex_owned(vp->v_interlock));
+               KASSERT(! (curlwp == vrele_lwp && defer));
+
                if (defer) {
                        /*
                         * Defer reclaim to the kthread; it's not safe to
                         * clean it here.  We donate it our last reference.
                         */
-                       KASSERT(mutex_owned(vp->v_interlock));
                        if ((flags & VRELEL_CHANGING_SET) != 0) {
                                KASSERT((vp->v_iflag & VI_CHANGING) != 0);
                                vp->v_iflag &= ~VI_CHANGING;