From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 07/15] writeback: split inode_wb_list_lock into
 bdi_writeback.list_lock
Date: Tue, 7 Jun 2011 16:03:19 -0700
Message-ID: <20110607160319.57f27481.akpm@linux-foundation.org>
References: <20110607213236.634026193@intel.com>
	<20110607213854.267319164@intel.com>
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Cc: Jan Kara <jack@suse.cz>, Christoph Hellwig <hch@lst.de>,
	Hugh Dickins <hughd@google.com>,
	Dave Chinner <david@fromorbit.com>,
	Christoph Hellwig <hch@infradead.org>,
	<linux-fsdevel@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
To: Wu Fengguang <fengguang.wu@intel.com>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <20110607213854.267319164@intel.com>
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List-Id: linux-fsdevel.vger.kernel.org

On Wed, 08 Jun 2011 05:32:43 +0800
Wu Fengguang <fengguang.wu@intel.com> wrote:

>  static void bdev_inode_switch_bdi(struct inode *inode,
>  			struct backing_dev_info *dst)
>  {
> -	spin_lock(&inode_wb_list_lock);
> +	struct backing_dev_info *old = inode->i_data.backing_dev_info;
> +
> +	if (unlikely(dst == old))		/* deadlock avoidance */
> +		return;

Why does this occur?