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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.
This commit is contained in:
mlelstv 2013-04-28 21:34:31 +00:00
parent 0b64d3196d
commit 220e532cc2
1 changed files with 15 additions and 4 deletions
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19
sys/kern/vfs_mount.c
View File

@ -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, struct lwp *l)
}
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);