[src/trunk]: src/sys/kern No, we can't elide the fs-wide rename lock for same...

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

details:   https://anonhg.NetBSD.org/src/rev/49f279a77f41
branches:  trunk
changeset: 782154:49f279a77f41
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Fri Oct 19 02:07:22 2012 +0000

description:
No, we can't elide the fs-wide rename lock for same-directory rename.

rename("a/b", "a/c") and rename("a/c/x", "a/b/y") will deadlock.

Darn.

diffstat:

 sys/kern/vfs_syscalls.c |  18 +++++++-----------
 1 files changed, 7 insertions(+), 11 deletions(-)

diffs (51 lines):

diff -r 8059d7a9c2f0 -r 49f279a77f41 sys/kern/vfs_syscalls.c
--- a/sys/kern/vfs_syscalls.c   Thu Oct 18 19:33:38 2012 +0000
+++ b/sys/kern/vfs_syscalls.c   Fri Oct 19 02:07:22 2012 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: vfs_syscalls.c,v 1.458 2012/10/12 02:37:20 riastradh Exp $     */
+/*     $NetBSD: vfs_syscalls.c,v 1.459 2012/10/19 02:07:22 riastradh Exp $     */
 
 /*-
  * Copyright (c) 2008, 2009 The NetBSD Foundation, Inc.
@@ -70,7 +70,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vfs_syscalls.c,v 1.458 2012/10/12 02:37:20 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_syscalls.c,v 1.459 2012/10/19 02:07:22 riastradh Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_fileassoc.h"
@@ -4041,11 +4041,9 @@
         * Take the vfs rename lock to avoid cross-directory screw cases.
         * Nothing is locked currently, so taking this lock is safe.
         */
-       if (fdvp != tdvp) {
-               error = VFS_RENAMELOCK_ENTER(mp);
-               if (error)
-                       goto abort1;
-       }
+       error = VFS_RENAMELOCK_ENTER(mp);
+       if (error)
+               goto abort1;
 
        /*
         * Now fdvp, fvp, tdvp, and (if nonnull) tvp are referenced,
@@ -4186,15 +4184,13 @@
         * So all we have left to do is to drop the rename lock and
         * destroy the pathbufs.
         */
-       if (fdvp != tdvp)
-               VFS_RENAMELOCK_EXIT(mp);
+       VFS_RENAMELOCK_EXIT(mp);
        goto out2;
 
 abort3:        if ((tvp != NULL) && (tvp != tdvp))
                VOP_UNLOCK(tvp);
 abort2:        VOP_UNLOCK(tdvp);
-       if (fdvp != tdvp)
-               VFS_RENAMELOCK_EXIT(mp);
+       VFS_RENAMELOCK_EXIT(mp);
 abort1:        VOP_ABORTOP(tdvp, &tnd.ni_cnd);
        vrele(tdvp);
        if (tvp != NULL)