netdev - Re: [PATCH 1/2] mlx4: remove unnecessary pci_set

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Message-ID: <20170815172149.GC15171@obsidianresearch.com>
Date:   Tue, 15 Aug 2017 11:21:49 -0600
From:   Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:     Leon Romanovsky <leonro@...lanox.com>
Cc:     Zhu Yanjun <yanjun.zhu@...cle.com>, saeedm@...lanox.com,
        matanb@...lanox.com, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, yuval.shaia@...cle.com
Subject: Re: [PATCH 1/2] mlx4: remove unnecessary pci_set_drvdata()

On Tue, Aug 15, 2017 at 10:13:36AM +0300, Leon Romanovsky wrote:
> On Tue, Aug 15, 2017 at 02:33:05AM -0400, Zhu Yanjun wrote:
> > The driver core clears the driver data to NULL after device_release
> > or on probe failure. Thus, it is not necessary to manually clear the
> > device driver data to NULL.
> >
> 
> It makes sense and I'm pretty sure that you are right, but I'm failing
> to find the function in device core which sets it to NULL. Can you help
> me and present the actual call stack to that code place?

http://elixir.free-electrons.com/linux/v4.13-rc1/source/drivers/base/dd.c#L840

The call to the remove callback is on line 833.

This is done after dropping devres, so you could allocate the drv data
inside a devm object and everything would unwind correctly.

In this case, the kfree is explicit, so I would advocate for still putting
the null near the kfree to minimize the time where a free'd pointer is
present - eg incase a devm callback or some other bug accidently
touches it.

Jason