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

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Date:	Tue, 10 Sep 2013 10:49:05 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	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>,
	Peng Tao <tao.peng@....com>, Peng Tao <bergwolf@...il.com>
Subject: Re: [PATCH] staging: Disable lustre file system for MIPS, SH, and XTENSA

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.

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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