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

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Message-ID: <20170815180038.GY24282@mtr-leonro.local>
Date:   Tue, 15 Aug 2017 21:00:38 +0300
From:   Leon Romanovsky <leonro@...lanox.com>
To:     Jason Gunthorpe <jgunthorpe@...idianresearch.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 11:21:49AM -0600, Jason Gunthorpe wrote:
> 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.

Thanks for the pointer. Will it be called in case of failure during
initialization too?

>
> 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

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