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Date: Fri, 28 Jun 2019 07:00:27 +0100
From: Al Viro <viro@zeniv.linux.org.uk>
Subject: [RFC] dget_parent() misuse in xfs_filestream_get_parent()
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To: Christoph Hellwig <hch@lst.de>
Cc: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org

	dget_parent() never returns NULL.  So this

        parent = dget_parent(dentry);
        if (!parent)
                goto out_dput;

        dir = igrab(d_inode(parent));
        dput(parent);

out_dput:

is obviously fishy.  What is that code trying to do?  Is that
"dentry might be a root of disconnected tree, in which case
we want xfs_filestream_get_parent() to return NULL"?  If so,
that should be

        parent = dget_parent(dentry);
        if (parent != dentry)
		dir = igrab(d_inode(parent));
        dput(parent);

If we want dentry itself, that dir = igrab(...) should be
unconditional.  I'm not familiar enough with that code,
and I'd rather not go into YAMassiveSideRTFS, so...