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Date: Thu, 28 Sep 2006 23:29:53 -0700
From: Andrew Morton <akpm@osdl.org>
To: NeilBrown <neilb@suse.de>, "David M. Grimes" <dgrimes@navisite.com>,
       Atal Shargorodsky <atal@codefidence.com>,
       Gilad Ben-Yossef <gilad@codefidence.com>
Cc: nfs@lists.sourceforge.net, linux-kernel@vger.kernel.org,
       Hugh Dickins <hugh@veritas.com>
Subject: Re: [PATCH 001 of 8] knfsd: Add nfs-export support to tmpfs
Message-Id: <20060928232953.6da08f19.akpm@osdl.org>
In-Reply-To: <1060929030839.24024@suse.de>
References: <20060929130518.23919.patches@notabene>
	<1060929030839.24024@suse.de>
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On Fri, 29 Sep 2006 13:08:39 +1000
NeilBrown <neilb@suse.de> wrote:

> +static int shmem_encode_fh(struct dentry *dentry, __u32 *fh, int *len, int connectable)
> +{
> +	struct inode *inode = dentry->d_inode;
> +
> +	if (*len < 2)
> +		return 255;
> +
> +	if (hlist_unhashed(&inode->i_hash)) {
> +		/* Unfortunately insert_inode_hash is not idempotent,
> +		 * so as we hash inodes here rather than at creation
> +		 * time, we need a lock to ensure we only try
> +		 * to do it once
> +		 */
> +		static DEFINE_SPINLOCK(lock);
> +		spin_lock(&lock);
> +		if (hlist_unhashed(&inode->i_hash))
> +			insert_inode_hash(inode);
> +		spin_unlock(&lock);
> +	}

This looks fishy.

How do we get two callers in here at the same time for the same inode?

Why don't other filesystems have the same problem?