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

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Date:   Sat, 18 Aug 2018 16:15:05 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Dave Jiang <dave.jiang@...el.com>,
        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 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