linux-kernel - Re: [PATCH] device-dax: don't set kobj parent during cdev init

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Message-ID: <c21c7b3d-81b8-d2ce-b5d0-42028984b93a@deltatee.com>
Date:   Sat, 11 Feb 2017 10:59:04 -0700
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Dan Williams <dan.j.williams@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Johannes Thumshirn <jthumshirn@...e.de>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Sajjan Vikas C <vikas.cha.sajjan@....com>,
        Arnd Bergmann <arnd@...db.de>, Jan Kara <jack@...e.cz>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>
Subject: Re: [PATCH] device-dax: don't set kobj parent during cdev init

On 11/02/17 01:56 AM, Dan Williams wrote:
> When the device is unregistered it invalidates all existing mappings,
> but the driver may continue to service vm fault requests until the
> final put of the cdev. Until that time the fault handler needs to be
> able to check dax_dev->alive. Since the final cdev put is handled by
> the vfs I use the cdev's kobject to keep the struct dax_dev instance
> alive.

I'm just taking a wild stab at this, but would it not make sense to just 
take a reference to the dax_dev device in dax_open and put it back it in 
dax_release? (Or perhaps, in the open/close of the vm_ops.) That way the 
structure won't be free'd until there are no users and alive will always 
be accessible.

It would also be a bit more clear as to what's going on because you are 
actually making a reference in filp->private_data.

Logan