Module Name: src
Committed By: mlelstv
Date: Sun Apr 28 21:34:31 UTC 2013
Modified Files:
src/sys/kern: vfs_mount.c
Log Message:
fix locking order mountlist_lock -> mnt_unmounting.
Set IMNT_GONE early to protect against concurrent dounmount()
and vfs_busy() before the mountpoint is removed from
mount list.
To generate a diff of this commit:
cvs rdiff -u -r1.18 -r1.19 src/sys/kern/vfs_mount.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/kern/vfs_mount.c
diff -u src/sys/kern/vfs_mount.c:1.18 src/sys/kern/vfs_mount.c:1.19
--- src/sys/kern/vfs_mount.c:1.18 Fri Apr 26 22:27:16 2013
+++ src/sys/kern/vfs_mount.c Sun Apr 28 21:34:31 2013
@@ -1,4 +1,4 @@
-/* $NetBSD: vfs_mount.c,v 1.18 2013/04/26 22:27:16 mlelstv Exp $ */
+/* $NetBSD: vfs_mount.c,v 1.19 2013/04/28 21:34:31 mlelstv Exp $ */
/*-
* Copyright (c) 1997-2011 The NetBSD Foundation, Inc.
@@ -67,7 +67,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vfs_mount.c,v 1.18 2013/04/26 22:27:16 mlelstv Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_mount.c,v 1.19 2013/04/28 21:34:31 mlelstv Exp $");
#include <sys/param.h>
#include <sys/kernel.h>
@@ -866,18 +866,29 @@ dounmount(struct mount *mp, int flags, s
}
mutex_exit(&mp->mnt_updating);
vfs_scrubvnlist(mp);
+
+ /*
+ * release mnt_umounting lock here, because other code calls
+ * vfs_busy() while holding the mountlist_lock.
+ *
+ * mark filesystem as gone to prevent further umounts
+ * after mnt_umounting lock is gone, this also prevents
+ * vfs_busy() from succeeding.
+ */
+ mp->mnt_iflag |= IMNT_GONE;
+ mutex_exit(&mp->mnt_unmounting);
+
mutex_enter(&mountlist_lock);
if ((coveredvp = mp->mnt_vnodecovered) != NULLVP)
coveredvp->v_mountedhere = NULL;
CIRCLEQ_REMOVE(&mountlist, mp, mnt_list);
- mp->mnt_iflag |= IMNT_GONE;
mutex_exit(&mountlist_lock);
if (TAILQ_FIRST(&mp->mnt_vnodelist) != NULL)
panic("unmount: dangling vnode");
if (used_syncer)
mutex_exit(&syncer_mutex);
vfs_hooks_unmount(mp);
- mutex_exit(&mp->mnt_unmounting);
+
vfs_destroy(mp); /* reference from mount() */
if (coveredvp != NULLVP) {
vrele(coveredvp);
