linux-kernel - Re: [PATCH] nvdimm: Replace the usage of a variable by a direct function call in nd_pfn

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Date:   Fri, 14 Apr 2023 12:14:58 -0700
From:   Alison Schofield <alison.schofield@...el.com>
To:     Markus Elfring <Markus.Elfring@....de>
Cc:     kernel-janitors@...r.kernel.org, nvdimm@...ts.linux.dev,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Vishal Verma <vishal.l.verma@...el.com>, cocci@...ia.fr,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] nvdimm: Replace the usage of a variable by a direct
 function call in nd_pfn_validate()

On Fri, Apr 14, 2023 at 06:50:59PM +0200, Markus Elfring wrote:
> >> The address of a data structure member was determined before
> >> a corresponding null pointer check in the implementation of
> >> the function “nd_pfn_validate”.
> >>
> >> Thus avoid the risk for undefined behaviour by replacing the usage of
> >> the local variable “parent_uuid” by a direct function call within
> >> a later condition check.
> >
> > Hi Markus,
> >
> > I think I understand what you are saying above, but I don't follow
> > how that applies here. This change seems to be a nice simplification,
> > parent_uuid, is used once, just grab it when needed.
> 
> Thanks for your positive feedback.

Hi Markus,

FYI - I'm a tiny bit taken aback that in response to me applying, and
providing feedback, on your patch, you respond with 2 links for me to
follow and cut off a chunk of my feedback.

Seems like it would taken the same amount of time to just answer my
two questions directly.

Was this part of a larger patch set? Andy's comment seems to indicate
that. Would have been nice to be CC'd on the cover letter.


More below...

> 
> 
> > What is the risk of undefined behavior?
> 
> See also:
> https://wiki.sei.cmu.edu/confluence/display/c/EXP34-C.+Do+not+dereference+null+pointers?focusedCommentId=405504137#comment-405504137

Where is the NULL pointer dereference here?

> 
> 
> >> This issue was detected by using the Coccinelle software.
> > Which cocci script?
> 
> See also:
> Reconsidering pointer dereferences before null pointer checks (with SmPL)
> https://lore.kernel.org/cocci/1a11455f-ab57-dce0-1677-6beb8492a257@web.de/
> https://sympa.inria.fr/sympa/arc/cocci/2023-04/msg00021.html
> 

The cocci script linked above does not seem to apply here.

> 
> How do you think about to review and improve any similarly affected software components?
> 
> Regards,
> Markus
>