ceph: don't return -ESTALE if there's still an open file

[ Upstream commit 878dabb64117406abd40977b87544d05bb3031fc ]

Similarly to commit 03f219041fdb ("ceph: check i_nlink while converting
a file handle to dentry"), this fixes another corner case with
name_to_handle_at/open_by_handle_at.  The issue has been detected by
xfstest generic/467, when doing:

 - name_to_handle_at("/cephfs/myfile")
 - open("/cephfs/myfile")
 - unlink("/cephfs/myfile")
 - sync; sync;
 - drop caches
 - open_by_handle_at()

The call to open_by_handle_at should not fail because the file hasn't been
deleted yet (only unlinked) and we do have a valid handle to it.  -ESTALE
shall be returned only if i_nlink is 0 *and* i_count is 1.

This patch also makes sure we have LINK caps before checking i_nlink.

Signed-off-by: Luis Henriques <lhenriques@suse.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Acked-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/ceph/export.c b/fs/ceph/export.c
index 79dc068..e088843 100644 (file)
--- a/fs/ceph/export.c
+++ b/fs/ceph/export.c
@@ -172,9 +172,16 @@ 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);
+       int err;
+
        if (IS_ERR(inode))
                return ERR_CAST(inode);
-       if (inode->i_nlink == 0) {
+       /* We need LINK caps to reliably check i_nlink */
+       err = ceph_do_getattr(inode, CEPH_CAP_LINK_SHARED, false);
+       if (err)
+               return ERR_PTR(err);
+       /* -ESTALE if inode as been unlinked and no file is open */
+       if ((inode->i_nlink == 0) && (atomic_read(&inode->i_count) == 1)) {
                iput(inode);
                return ERR_PTR(-ESTALE);
        }