linux-kernel - Re: [PATCH] libata-eh: Use switch() instead of sparse array for protocol strings

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Message-ID: <CAMuHMdUVtQOJYfQsspSk9+v-4abGf+OTSMWEfzXvGLu9namqZg@mail.gmail.com>
Date:   Mon, 9 Jan 2017 21:28:12 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        "linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] libata-eh: Use switch() instead of sparse array for
 protocol strings

Hi Tejun,

On Mon, Jan 9, 2017 at 8:41 PM, Tejun Heo <tj@...nel.org> wrote:
> On Mon, Jan 09, 2017 at 07:25:31PM +0100, Geert Uytterhoeven wrote:
>> On Mon, Jan 9, 2017 at 6:31 PM, Tejun Heo <tj@...nel.org> wrote:
>> > On Mon, Jan 09, 2017 at 09:27:23AM -0800, Christoph Hellwig wrote:
>> >> On Mon, Jan 09, 2017 at 05:30:02PM +0100, Geert Uytterhoeven wrote:
>> >> > > ata_force_param_buf is __initdata and shouldn't really matter.
>> >> >
>> >> > It mainly matters because of e.g. bootloader limitations.
>> >>
>> >> Do we need a full 4k for the force parameters?  What would a typical
>> >> command line for it look like?
>> >
>> > Maybe a couple hundreds bytes at max, but it's a bit weird to restrict
>> > this given that it is bss, not gigantic and __initdata.  What kind of
>> > bootloader limitations are we talking about?
>>
>> Some boot loaders start overwriting themselves or the passed DTB if the
>> kernel becomes too big.
>> If I'm not mistaken, bss is still expanded early (verified, increasing bss
>> can trigger the above problem).
>
> So, to avoid that, we can just kmalloc and kfree the buffer, but it
> seems like a silly complication to work around bugs in some
> bootloaders.  There are many places in kernel where we're liberal
> about __initdata which is great.  I'm not sure complicating all those
> places for a broken bootloader is a good idea.

Sure. We cannot avoid that kernels (esp. multiplatform) keep on growing.

But when I see a new 4KiB-sized buffer, i'm always suspicious...
A few years ago, I caught someone miscalculating shifts, leading
to a static buffer that was 256 times larger than intended ;-)

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds