linux-kernel - Re: [PATCH] staging: Disable lustre file system for MIPS, SH, and XTENSA

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Date:	Wed, 11 Sep 2013 01:15:49 +0800
From:	Peng Tao <bergwolf@...il.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Guenter Roeck <linux@...ck-us.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"David S. Miller" <davem@...emloft.net>,
	Christoph Hellwig <hch@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	driverdevel <devel@...verdev.osuosl.org>
Subject: Re: [PATCH] staging: Disable lustre file system for MIPS, SH, and XTENSA

On Tue, Sep 10, 2013 at 4:49 PM, Geert Uytterhoeven
<geert@...ux-m68k.org> wrote:
> On Mon, Sep 9, 2013 at 10:06 PM, Guenter Roeck <linux@...ck-us.net> wrote:
>>> [*] Why does m68k allmodconfig still succeed on kissb???
>>>     It does fail for me, as m68k's copy_from_user_page() calls
>>>     flush_icache_user_range(), which is not exported.
>>>
>> I don't see a build failure in m68k:allmodconfig either.
>>
>> flush_icache_user_range() is called from copy_to_user_page(), not from
>> copy_from_user_page(). copy_from_user_page() calls flush_cache_page()
>> which calls __flush_cache_030(). The first is inline, the second is
>> assembler, so I would expect it to work. Which doesn't answer
>> the question why it fails for you.
>
> Sorry, I meant copy_to_user_page().
>
> I tried with 2.6.3 from crosstool, and it succeeded, too.
>
> Turns out cfs_access_process_vm() is called with write=0 only.
> Gcc 2.6.3 optimizes away the write != 0 branch (which calls copy_to_user_page()
> and thus flush_icache_user_range()), while gcc 4.1.2 doesn't do that.
> Mystery solved.
>
Thanks for chasing down the root cause. I was also wondering why I
didn't see this when building on MIPS some time ago.

Thanks,
Tao

> 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
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