linux-kernel - Re: [GIT PULL]: libnvdimm updates for v4.19-rc1

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Message-ID: <4b2eaec3-7dd7-5b68-d0e1-3d0834b83c8b@intel.com>
Date:   Mon, 20 Aug 2018 10:21:43 -0700
From:   Dave Jiang <dave.jiang@...el.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>
Subject: Re: [GIT PULL]: libnvdimm updates for v4.19-rc1



On 08/18/2018 04:15 PM, Linus Torvalds wrote:
> On Fri, Aug 17, 2018 at 9:17 AM Jiang, Dave <dave.jiang@...el.com> wrote:
>>
>> Please pull to receive libnvdimm contributions for v4.19-rc1
> 
> So I don't care about the libnvdimm code itself, but when you guys add
> code to the core mm/ code, I start looking.
> 
> And when I then see shit like this:
> 
>         if (is_zone_device_page(p))
>                 tk->size_shift = ilog2(dev_pagemap_mapping_size(p, vma));
> 
> I go "No".
> 
> There's two issues with this:
> 
>  - the damn thing can return 0, which would be an error for ilog2, and
> the result is undefined
> 
>    You never check for errors. There's a check for tk->size_shift ==
> 0, but is that actually the guaranteed return value of ilog2(0)? No.
> 
>  - there is exactly one user of dev_pagemap_mapping_size(), and the above is it.
> 
>    Why the hell didn't that function just return the number of bits to
> begin with?
> 
> I do not care if you screw up your own particular driver that much.
> 
> But when I see a pull request with complete and utter garbage in the
> core mm part, I will not pull.
> 
> This is not acceptable.
> 
> Pulled, merge conflict fixed, and then immediately unpulled again.
> 
> I do not want to *EVER* see these kinds of patches to core MM code.
> And I'm not gfoing to pull these patches or anythinig that looks like
> it has any trace of this shit.
> 
> I get upset, because dammit, I expect better. I don't want to go "oh,
> this changes core code, let's just skim over the patches" and
> immediately find something fundamentally broken like this.
> 
>                Linus
>

Linus,
I have addressed the mistake by changing the function directly to return
PXX_SHIFT instead of size and removed the offending ilog2() call. I have
pushed the branch to kernel.org nvdimm tree for linux-next soaking. If
it's acceptable to you I'll send the pull request again later this week
for 4.19 inclusion. Thank you!