[PATCH] ceph: fail the open_by_handle_at() if the dentry is being unlinked

[xiubli@redhat.com]

From: Xiubo Li <xiubli@redhat.com>

When unlinking a file the kclient will send a unlink request to MDS
by holding the dentry reference, and then the MDS will return 2 replies,
which are unsafe reply and a deferred safe reply.

After the unsafe reply received the kernel will return and succeed
the unlink request to user space apps.

Only when the safe reply received the dentry's reference will be
released. Or the dentry will only be unhashed from dcache. But when
the open_by_handle_at() begins to open the unlinked files it will
succeed.

URL: https://tracker.ceph.com/issues/56524
Signed-off-by: Xiubo Li <xiubli@redhat.com>
---
 fs/ceph/export.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/fs/ceph/export.c b/fs/ceph/export.c
index 0ebf2bd93055..7d2ae977b8c9 100644
--- a/fs/ceph/export.c
+++ b/fs/ceph/export.c
@@ -182,6 +182,7 @@ struct inode *ceph_lookup_inode(struct super_block *sb, u64 ino)
 static struct dentry *__fh_to_dentry(struct super_block *sb, u64 ino)
 {
 	struct inode *inode = __lookup_inode(sb, ino);
+	struct dentry *dentry;
 	int err;
 
 	if (IS_ERR(inode))
@@ -197,7 +198,15 @@ static struct dentry *__fh_to_dentry(struct super_block *sb, u64 ino)
 		iput(inode);
 		return ERR_PTR(-ESTALE);
 	}
-	return d_obtain_alias(inode);
+
+	/* -ESTALE if the dentry is unhashed, which should being released */
+	dentry = d_obtain_alias(inode);
+	if (d_unhashed(dentry)) {
+		dput(dentry);
+		return ERR_PTR(-ESTALE);
+	}
+
+	return dentry;
 }
 
 static struct dentry *__snapfh_to_dentry(struct super_block *sb,
-- 
2.36.0.rc1