[PATCH 3.19 159/177] NFS: Dont invalidate a submounted dentry in nfs_prime_dcache()

Greg Kroah-Hartman
2015-03-16T14:18:36Z

From: Trond Myklebust <trond.myklebust@primarydata.com>

commit 6c441c254eea2354d686be7f5544bcd79fb6a61f upstream.

If we're traversing a directory which contains a submounted filesystem,
or one that has a referral, the NFS server that is processing the READDIR
request will often return information for the underlying (mounted-on)
directory. It may, or may not, also return filehandle information.

If this happens, and the lookup in nfs_prime_dcache() returns the
dentry for the submounted directory, the filehandle comparison will
fail, and we call d_invalidate(). Post-commit 8ed936b5671bf
("vfs: Lazily remove mounts on unlinked files and directories."), this
means the entire subtree is unmounted.

The following minimal patch addresses this problem by punting on
the invalidation if there is a submount.

Kudos to Neil Brown <neilb@suse.de> for having tracked down this
issue (see link).

Reported-by: Nix <nix@esperi.org.uk>
Link: http://lkml.kernel.org/r/87iofju9ht.fsf@spindle.srvr.nix
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/nfs/dir.c | 6 ++++++
1 file changed, 6 insertions(+)

--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -469,6 +469,8 @@ void nfs_prime_dcache(struct dentry *par
struct inode *inode;
int status;

+ if (!(entry->fattr->valid & NFS_ATTR_FATTR_FSID))
+ return;
if (filename.name[0] == '.') {
if (filename.len == 1)
return;
@@ -479,6 +481,10 @@ void nfs_prime_dcache(struct dentry *par

dentry = d_lookup(parent, &filename);
if (dentry != NULL) {
+ /* Is there a mountpoint here? If so, just exit */
+ if (!nfs_fsid_equal(&NFS_SB(dentry->d_sb)->fsid,
+ &entry->fattr->fsid))
+ goto out;
if (nfs_same_file(dentry, entry)) {
nfs_set_verifier(dentry, nfs_save_change_attribute(dir));
status = nfs_refresh_inode(dentry->d_inode, entry->fattr);