linux-kernel - [ 16/17] vfs: d_obtain_alias() needs to use "/" as default name.

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Date:	Mon, 12 Aug 2013 23:36:02 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, NeilBrown <neilb@...e.de>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ben Hutchings <ben@...adent.org.uk>
Subject: [ 16/17] vfs: d_obtain_alias() needs to use "/" as default name.

3.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: NeilBrown <neilb@...e.de>

commit b911a6bdeef5848c468597d040e3407e0aee04ce upstream.

NFS appears to use d_obtain_alias() to create the root dentry rather than
d_make_root.  This can cause 'prepend_path()' to complain that the root
has a weird name if an NFS filesystem is lazily unmounted.  e.g.  if
"/mnt" is an NFS mount then

 { cd /mnt; umount -l /mnt ; ls -l /proc/self/cwd; }

will cause a WARN message like
   WARNING: at /home/git/linux/fs/dcache.c:2624 prepend_path+0x1d7/0x1e0()
   ...
   Root dentry has weird name <>

to appear in kernel logs.

So change d_obtain_alias() to use "/" rather than "" as the anonymous
name.

Signed-off-by: NeilBrown <neilb@...e.de>
Cc: Trond Myklebust <Trond.Myklebust@...app.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
[bwh: Backported to 3.2: use named initialisers instead of QSTR_INIT()]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/dcache.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1556,7 +1556,7 @@ EXPORT_SYMBOL(d_find_any_alias);
  */
 struct dentry *d_obtain_alias(struct inode *inode)
 {
-	static const struct qstr anonstring = { .name = "" };
+	static const struct qstr anonstring = { .name = "/", .len = 1 };
 	struct dentry *tmp;
 	struct dentry *res;
 


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