Since commit ff17fa561a04 ("d_invalidate(): unhash immediately")
immediately unhashes the dentry, we'll never return the mountpoint in
lookup_mountpoint(), which can lead to an unbreakable loop in
d_invalidate().
I have reports of NFS clients getting into this condition after the server
removes an export of an existing mount created through follow_automount(),
but I suspect there are various other ways to produce this problem if we
hunt down users of d_invalidate(). For example, it is possible to get into
this state by using XFS' d_invalidate() call in xfs_vn_unlink():
truncate -s 100m img{1,2}
mkfs.xfs -q -n version=ci img1
mkfs.xfs -q -n version=ci img2
mkdir -p /mnt/xfs
mount img1 /mnt/xfs
mkdir /mnt/xfs/sub1
mount img2 /mnt/xfs/sub1
cat > /mnt/xfs/sub1/foo &
umount -l /mnt/xfs/sub1
mount img2 /mnt/xfs/sub1
mount --make-private /mnt/xfs
mkdir /mnt/xfs/sub2
mount --move /mnt/xfs/sub1 /mnt/xfs/sub2
rmdir /mnt/xfs/sub1
Fix this by moving the check for an unlinked dentry out of the
detach_mounts() path.
Fixes: ff17fa561a04 ("d_invalidate(): unhash immediately")
Signed-off-by: Benjamin Coddington <bcodding@xxxxxxxxxx>
---
fs/namespace.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/fs/namespace.c b/fs/namespace.c
index bd2f4c68506a..79cf26d9866a 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -780,9 +780,6 @@ static struct mountpoint *lookup_mountpoint(struct dentry *dentry)
hlist_for_each_entry(mp, chain, m_hash) {
if (mp->m_dentry == dentry) {
- /* might be worth a WARN_ON() */
- if (d_unlinked(dentry))
- return ERR_PTR(-ENOENT);
mp->m_count++;
return mp;
}
@@ -795,7 +792,11 @@ static struct mountpoint *get_mountpoint(struct dentry *dentry)
struct mountpoint *mp, *new = NULL;
int ret;
+
if (d_mountpoint(dentry)) {
+ /* might be worth a WARN_ON() */
+ if (d_unlinked(dentry))
+ return ERR_PTR(-ENOENT);
mountpoint:
read_seqlock_excl(&mount_lock);
mp = lookup_mountpoint(dentry);
--
2.14.3
