Date: Fri, 20 Apr 2007 18:51:11 -0700 From: Maxim Sobolev <sobomax@FreeBSD.org> To: "current@freebsd.org" <current@FreeBSD.org>, freebsd-fs@FreeBSD.org Subject: Bug in the unmounting code Message-ID: <46296E0F.2070202@FreeBSD.org>
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Hi,
I have noticed that there is a bug in unmounting code which could make
filesystem unmountable when its parent filesystem has been forcefully
unmounted. Following is quick way to reproduce the problem:
[sobomax@pioneer ~]$ sudo mkdir -p /tmp/1/2
[sobomax@pioneer ~]$ sudo mkdir /tmp/3
[sobomax@pioneer ~]$ sudo mount_nullfs /tmp/1 /tmp/3
[sobomax@pioneer ~]$ sudo mount_nullfs /tmp/1 /tmp/3/2
[sobomax@pioneer ~]$ sudo umount -f /tmp/3
[sobomax@pioneer ~]$ sudo mount -v
/tmp/1 on /tmp/3/2 (nullfs, local, fsid 03ff000202000000)
[sobomax@pioneer ~]$ sudo umount 03ff000202000000
umount: unmount of /tmp/3/2 failed: No such file or directory
umount: retrying using path instead of file system ID
umount: unmount of /tmp/3/2 failed: No such file or directory
Investigation has revealed that in this case vn_lock() call fails with
ENOENT due to the following piece of code:
vn_lock()
[...]
if (error == 0 && vp->v_iflag & VI_DOOMED &&
(flags & LK_RETRY) == 0) {
VOP_UNLOCK(vp, 0, td);
error = ENOENT;
break;
}
[...]
Addition of LK_RETRY flag fixed the problem, but my knowledge of VFS is
quite limited so that I would appreciate if somebody could verify that
the fix below won't have any undesirable effects.
-Maxim
--- vfs_mount.c 2007/04/21 01:40:53 1.1
+++ vfs_mount.c 2007/04/21 01:41:09
@@ -1155,7 +1155,7 @@
mnt_gen_r = mp->mnt_gen;
VI_LOCK(coveredvp);
vholdl(coveredvp);
- error = vn_lock(coveredvp, LK_EXCLUSIVE | LK_INTERLOCK, td);
+ error = vn_lock(coveredvp, LK_EXCLUSIVE | LK_INTERLOCK |
LK_RETRY, td);
vdrop(coveredvp);
/*
* Check for mp being unmounted while waiting for the
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