[src/trunk]: src/sys/kern redo vfs_lookup.c rev.1.126.

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

details:   https://anonhg.NetBSD.org/src/rev/1171e22008de
branches:  trunk
changeset: 769161:1171e22008de
user:      yamt <yamt%NetBSD.org@localhost>
date:      Thu Sep 01 15:31:27 2011 +0000

description:
redo vfs_lookup.c rev.1.126.
when crossing a mount point, don't keep the parent vnode locked.
ie. don't lock a vnode while holding another vnode which belongs to a
different filesystem.  otherwise we propagate slowness (or deadness) of a
filesystem to another via vnode lock chain.

diffstat:

 sys/kern/vfs_lookup.c |  48 ++++++++++++++++++++++++++++++++++++------------
 1 files changed, 36 insertions(+), 12 deletions(-)

diffs (92 lines):

diff -r 8e9f83d6bcc2 -r 1171e22008de sys/kern/vfs_lookup.c
--- a/sys/kern/vfs_lookup.c     Thu Sep 01 15:15:06 2011 +0000
+++ b/sys/kern/vfs_lookup.c     Thu Sep 01 15:31:27 2011 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: vfs_lookup.c,v 1.189 2011/08/13 19:40:02 riastradh Exp $       */
+/*     $NetBSD: vfs_lookup.c,v 1.190 2011/09/01 15:31:27 yamt Exp $    */
 
 /*
  * Copyright (c) 1982, 1986, 1989, 1993
@@ -37,7 +37,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vfs_lookup.c,v 1.189 2011/08/13 19:40:02 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_lookup.c,v 1.190 2011/09/01 15:31:27 yamt Exp $");
 
 #include "opt_magiclinks.h"
 
@@ -1040,11 +1040,16 @@
               (cnp->cn_flags & NOCROSSMOUNT) == 0) {
                error = vfs_busy(mp, NULL);
                if (error != 0) {
-                       vput(foundobj);
+                       if (searchdir != foundobj) {
+                               vput(foundobj);
+                       } else {
+                               vrele(foundobj);
+                       }
                        goto done;
                }
-               KASSERT(searchdir != foundobj);
-               VOP_UNLOCK(searchdir);
+               if (searchdir != foundobj) {
+                       VOP_UNLOCK(searchdir);
+               }
                vput(foundobj);
                error = VFS_ROOT(mp, &foundobj);
                vfs_unbusy(mp, false, NULL);
@@ -1052,9 +1057,22 @@
                        vn_lock(searchdir, LK_EXCLUSIVE | LK_RETRY);
                        goto done;
                }
-               VOP_UNLOCK(foundobj);
-               vn_lock(searchdir, LK_EXCLUSIVE | LK_RETRY);
-               vn_lock(foundobj, LK_EXCLUSIVE | LK_RETRY);
+               /*
+                * avoid locking vnodes from two filesystems because it's
+                * prune to deadlock.  eg. when using puffs.
+                * also, it isn't a good idea to propagate slowness of a
+                * filesystem up to the root directory.
+                * for now, only handle the common case.  (ie. foundobj is VDIR)
+                */
+               if (foundobj->v_type == VDIR) {
+                       vrele(searchdir);
+                       *newsearchdir_ret = searchdir = foundobj;
+                       vref(searchdir);
+               } else {
+                       VOP_UNLOCK(foundobj);
+                       vn_lock(searchdir, LK_EXCLUSIVE | LK_RETRY);
+                       vn_lock(foundobj, LK_EXCLUSIVE | LK_RETRY);
+               }
        }
 
        *foundobj_ret = foundobj;
@@ -1240,9 +1258,11 @@
                 * Check for directory, if the component was
                 * followed by a series of slashes.
                 */
-               if ((foundobj->v_type != VDIR) && (cnp->cn_flags & REQUIREDIR)) {
-                       KASSERT(foundobj != searchdir);
-                       if (searchdir) {
+               if ((foundobj->v_type != VDIR) &&
+                   (cnp->cn_flags & REQUIREDIR)) {
+                       if (searchdir == foundobj) {
+                               vrele(searchdir);
+                       } else {
                                vput(searchdir);
                        }
                        vput(foundobj);
@@ -1545,7 +1565,11 @@
        vref(startdir);
        vn_lock(startdir, LK_EXCLUSIVE | LK_RETRY);
        error = lookup_once(state, startdir, &startdir, &foundobj);
-       vput(startdir);
+       if (error == 0 && startdir == foundobj) {
+               vrele(startdir);
+       } else {
+               vput(startdir);
+       }
        if (error) {
                goto bad;
        }