linux-kernel - Re: [PATCH] libnvdimm: remove redundant assignment to pointer 'dev'

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Date:   Mon, 5 Feb 2018 14:35:44 -0700
From:   Ross Zwisler <ross.zwisler@...ux.intel.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Colin King <colin.king@...onical.com>,
        linux-nvdimm@...ts.01.org, kernel-janitors@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] libnvdimm: remove redundant assignment to pointer 'dev'

On Mon, Feb 05, 2018 at 10:44:07AM -0800, Dan Williams wrote:
> On Mon, Feb 5, 2018 at 10:20 AM, Ross Zwisler
> <ross.zwisler@...ux.intel.com> wrote:
> > On Mon, Feb 05, 2018 at 02:08:52PM +0000, Colin King wrote:
> >> From: Colin Ian King <colin.king@...onical.com>
> >>
> >> Pointer dev is being assigned a value that is never read, it is being
> >> re-assigned the same value later on, hence the initialization is redundant
> >> and can be removed.
> >>
> >> Cleans up clang warning:
> >> drivers/nvdimm/pfn_devs.c:307:17: warning: Value stored to 'dev' during
> >> its initialization is never read
> >>
> >> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> >
> > Reviewed-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
> >
> > More importantly this fixes a potential NULL pointer dereference.  nd_pfn
> > is checked for NULL a few lines down, but we would have crashed here trying to
> > get nd_pfn->dev.
> >
> 
> No we wouldn't crash. We're just calculating the address, not
> de-referencing a NULL pointer.

Ah, yep, you're right of course.  This is exactly how offsetof() is
implemented in some architectures.  Thanks.