Al, would you be willing to take a look at this one? Ben On 3 Oct 2018, at 10:18, Benjamin Coddington wrote:
v2: less whitespace 8<------------------------------------------------------------------------ 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 intothis 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 | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index bd2f4c68506a..ad8feb9371f2 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; }@@ -796,6 +793,9 @@ static struct mountpoint *get_mountpoint(struct dentry *dentry)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
