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

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Message-ID: <20170109194100.GH12827@mtj.duckdns.org>
Date:   Mon, 9 Jan 2017 14:41:00 -0500
From:   Tejun Heo <tj@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.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

Hello, Geert.

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.

Thanks.

-- 
tejun