From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH] ch: add refcounting
Date: Thu, 10 Apr 2014 04:51:57 -0700
Message-ID: <20140410115157.GA8564@infradead.org>
References: <1396938437-29616-1-git-send-email-hare@suse.de>
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To: Hannes Reinecke <hare@suse.de>
Cc: James Bottomley <jbottomley@parallels.com>, linux-scsi@vger.kernel.org

>  static int
>  ch_release(struct inode *inode, struct file *file)
>  {
>  	scsi_changer *ch = file->private_data;
>  
>  	scsi_device_put(ch->device);
> +	ch->device = NULL;
>  	file->private_data = NULL;
> +	kref_put(&ch->ref, ch_destroy);

Any reason you need to put the scsi_device here already?  Defering
this would give you much eaiser life time rules, and no need to
deal with a NULL ch->device ever.