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@xxxxxxx> for having tracked down this
issue (see link).
Reported-by: Nix <nix@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/87iofju9ht.fsf@xxxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx # 3.18+
Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
---
fs/nfs/dir.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 9b0c55cb2a2e..0da617a61c0b 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -479,6 +479,10 @@ void nfs_prime_dcache(struct dentry *parent, struct nfs_entry *entry)
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);
--
2.1.0
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