From mboxrd@z Thu Jan  1 00:00:00 1970
From: Al Viro <viro@ZenIV.linux.org.uk>
Subject: Re: [PATCH] vfs: Fix, simpliy and stop using d_dname for the
 /proc/*/ns/* files.
Date: Thu, 21 May 2015 00:23:25 +0100
Message-ID: <20150520232325.GA7232@ZenIV.linux.org.uk>
References: <20150515185820.GQ20468@ycc.fr>
 <20150520100557.GB32189@mew>
 <87bnhedhw5.fsf_-_@x220.int.ebiederm.org>
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Cc: Omar Sandoval <osandov@osandov.com>,
	Ivan Delalande <colona@arista.com>,
	linux-fsdevel@vger.kernel.org
To: "Eric W. Biederman" <ebiederm@xmission.com>
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On Wed, May 20, 2015 at 05:05:30PM -0500, Eric W. Biederman wrote:

> -	dentry = d_alloc_pseudo(mnt->mnt_sb, &qname);
> +	dentry = d_alloc_name(mnt->mnt_root, name);
>  	if (!dentry) {
>  		iput(inode);
>  		mntput(mnt);
>  		return ERR_PTR(-ENOMEM);
>  	}
> -	d_instantiate(dentry, inode);
> +	d_add(dentry, inode);

Careful - that might have non-trivial effects.  Namely, you are making
the root dentry of that sucker a contention point and adding to hash
pollution...  It's probably not going to cause visible problems, but
it's worth profiling just to be sure.

Besides, you are violating a bunch of rules here - several hashed
children of the same directory with the same name all at once...
not nice.