Date:   Tue, 7 May 2019 09:54:12 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <bbrezillon@...nel.org>,
        Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] mtd: cfi_util: mark expected switch fall-throughs

Hi all,

Thanks a lot for this, Richard:

https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git/log/?h=mtd%2Fnext&qt=grep&q=fall-through

There are only two of these warnings left to be addressed in
MTD[1]:

        > @@ -3280,12 +3280,14 @@ static void onenand_check_features(struct mtd_info *mtd)
        >                       if ((this->version_id & 0xf) == 0xe)
        >                               this->options |= ONENAND_HAS_NOP_1;
        >               }
        > +             /* fall through */
        >
        >       case ONENAND_DEVICE_DENSITY_2Gb:
        >               /* 2Gb DDP does not have 2 plane */
        >               if (!ONENAND_IS_DDP(this))
        >                       this->options |= ONENAND_HAS_2PLANE;
        >               this->options |= ONENAND_HAS_UNLOCK_ALL;
        > +             /* fall through */

        This looks strange.

        In ONENAND_DEVICE_DENSITY_2Gb:
        ONENAND_HAS_UNLOCK_ALL is set unconditionally.

        But then, under ONENAND_DEVICE_DENSITY_1Gb, the same option is set only
        if process is evaluated to true.

        Same problem with ONENAND_HAS_2PLANE:
        - it is set in ONENAND_DEVICE_DENSITY_4Gb only if ONENAND_IS_DDP()
        - it is unset in ONENAND_DEVICE_DENSITY_2Gb only if !ONENAND_IS_DDP()

        Maybe this portion should be reworked because I am unsure if this is a
        missing fall through or a bug.


Thanks
--
Gustavo

[1] https://lore.kernel.org/patchwork/patch/1036251/

On 4/16/19 3:49 PM, Gustavo A. R. Silva wrote:
> Hi Miquel,
> 
> On 4/16/19 12:24 PM, Miquel Raynal wrote:
>> Hi Gustavo,
>>
>> "Gustavo A. R. Silva" <gustavo@...eddedor.com> wrote on Mon, 15 Apr
>> 2019 07:57:11 -0500:
>>
>>> Hi Miquel,
>>>
>>> On 4/15/19 3:44 AM, Miquel Raynal wrote:
>>>> Hi Gustavo,
>>>>
>>>> "Gustavo A. R. Silva" <gustavo@...eddedor.com> wrote on Wed, 10 Apr
>>>> 2019 16:16:51 -0500:
>>>>   
>>>>> Hi all,
>>>>>
>>>>> If no one cares I'll add this to my tree for 5.2.  
>>>>
>>>> Which tree are you talking about?
>>>>   
>>>
>>> This one:
>>>
>>> https://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux.git/log/?h=for-next/kspp
>>>
>>>> Please let the MTD maintainers take patches through their tree. We
>>>> might be late but this is definitely not a good reason to bypass us.
>>>>   
>>> It's a bit confusing when patches are being ignored for more than two
>>> months:
>>>
>>> https://lore.kernel.org/patchwork/patch/1040099/
>>> https://lore.kernel.org/patchwork/patch/1040100/
>>> https://lore.kernel.org/patchwork/patch/1040098/
>>>
>>
>> Patches posted at -rc6 right before the last release? Come on! Gustavo,
>> we always spend more time for you than for other contributors because we
>> do not trust your changes. We could apply them blindly but we don't do
>> that for other (worthy) contributions, so why shall we do it for you?
>>
> 
> Oh, I didn't know about that. You don't have to blindly trust me.
> I sincerely think people should always double check any changes,
> regardless of their level of trust in a particular person/entity.
> 
> Anyway, I really appreciate your sincerity because now I think we can
> come up with a good strategy to collaborate with each other smoothly.
> 
> It seems to me that the root cause for this lack of trust, and, maybe
> even despite towards these type of patches, is basically misunderstanding
> of what I'm trying to accomplish and, more importantly, how I do it.
> 
>> I think you could at least flag these changes as "automatic and
>> unverified" in the commit log so that when git blaming, people could
>> know that the additional explicit /* fallthrough */ comment might be
>> wrong and was just added in order to limit the number of warnings when
>> enabling the extra GCC warning.
>>
> 
> I don't do that because that's not how I'm tackling this task.
> 
> I'm not sending these patches with the intention of merely accumulate
> contributions --and I'm not saying you say so, this is just for
> clarification-- or because of a lack of more technically interesting
> things to do in the kernel --this is certainly not the only thing I'm
> working on.  What I'm trying to accomplish is to be able to add
> -Wimplicit-fallthrough to the build so that the kernel will stay
> entirely free of this class of bug going forward; is that simple. Now,
> why is that? because sometimes people forget to place a break/return
> and a bug is introduced, and it could take up to 7 years to fix it [1].
> 
> Now, I really try to determine if I'm dealing with a false positive or
> an actual bug every time. I read the code and try to understand the
> context around which each warning is reported. You can tell it's not
> the most sexy and glamorous thing. And a static analyzer is clearly not
> sophisticated enough to spot actual bugs in this situation, not even
> the Coccinelle tool.
> 
> I had a similar conversation with a wireless maintainer a while ago. He
> claimed I was not even looking at the code and that I was blindly using
> a transformation tool [2]. Please, take a look at it, so you can better
> understand my workflow.
> 
> I have gone through this process of reading code all over the tree and
> trying to understand it hundreds of times; there were more than 2000 of
> these warnings at the time I started working on this, and there are are
> around 50 left in linux-next.  Of course, the vast majority of cases have
> resulted to be obvious false positives, but it's me who have determined
> that, by auditing each case, so I haven't blindly placed any fall-through
> comment.
> 
> Now, have I made any mistake? Of course! but I have also amended it
> immediately [3][4]. And the number of bugs I have fixed while working
> on this task is much bigger.  A clear example of how hard this can be is
> documented in this thread, in which you, being an MTD maintainer, cannot
> clearly determine if this is a false positive or an actual bug [5]. It
> can be troublesome for you for a number of reasons --I'm not judging that.
> I'm trying to illustrate the magnitude of the task as a whole.
> 
> So, this patches together with the related bugfixes are part of that
> whole. And, although sometimes painful for everyone, that whole is
> what's important, and worth it.
> 
>>> Certainly, Richard Weinberger replied to this one. But I couldn't
>>> find a tree to which this patch was applied, in case it actually
>>> was.
>>>
>>> It's a common practice for maintainers to reply saying that a patch
>>> has been finally applied, and in most cases they also explicitly
>>> mention the tree and branch to which it was applied. All this info
>>> is really helpful for people working all over the tree.
>>
>> It is common practice for contributors to understand what they
>> are doing before submitting a change and this is something that you
>> clearly don't try to do.
>>
> 
> This is too much to say, and sadly, it's not uncommon for even the most
> senior people to assume others don't even make an effort to think through
> their work, before at least asking. But I have already explained myself
> above.
> 
> Regarding this:
> 
>> Patches posted at -rc6 right before the last release? Come on! Gustavo,
> 
> I don't expect people to send an urgent pull-request to merge this
> patches into mainline as soon as they arrive, and I have never requested
> such thing.
> 
> Lastly, what I really want we *all* get out of this conversation is a
> better way to collaborate with each other.  For me, and I guess for most
> contributors, it's good enough to have a confirmation that the accepted
> patch has been applied to a certain branch in a certain tree. I understand
> this may sound like an special request, in particular because, currently,
> the number of people working all over the tree is not that big, so it
> is not that critical for maintainers to adopt certain practices that
> benefits this small group of contributors, but thanks to recent initiatives
> as The Linux Kernel Mentorship project I think this is going to change and
> it will force us all to evolve in the right direction.
> 
> By the way, notice that these are the last patches for MTD. :)
> 
> Thank you
> --
> Gustavo
> 
> References:
> 
> [1] https://lore.kernel.org/patchwork/patch/1042976/
> [2] https://lore.kernel.org/patchwork/patch/1002568/
> [3] https://lore.kernel.org/patchwork/patch/970617/
> [4] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v5.1-rc5&id=ad0eaee6195db1db1749dd46b9e6f4466793d178
> [5] https://lore.kernel.org/patchwork/patch/1036251/
> 
> 
> 

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