Re: [PATCH] ARM: fix __get_user_check() in case uaccess_* calls are not inlined

[Nicolas Saenz Julienne <nsaenzjulienne@suse.de>]

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On Mon, 2019-09-30 at 14:59 +0900, Masahiro Yamada wrote:
> KernelCI reports that bcm2835_defconfig is no longer booting since
> commit ac7c3e4ff401 ("compiler: enable CONFIG_OPTIMIZE_INLINING
> forcibly"):
> 
>   https://lkml.org/lkml/2019/9/26/825
> 
> I also received a regression report from Nicolas Saenz Julienne:
> 
>   https://lkml.org/lkml/2019/9/27/263
> 
> This problem has cropped up on arch/arm/config/bcm2835_defconfig
> because it enables CONFIG_CC_OPTIMIZE_FOR_SIZE. The compiler tends
> to prefer not inlining functions with -Os. I was able to reproduce
> it with other boards and defconfig files by manually enabling
> CONFIG_CC_OPTIMIZE_FOR_SIZE.
> 
> The __get_user_check() specifically uses r0, r1, r2 registers.
> So, uaccess_save_and_enable() and uaccess_restore() must be inlined
> in order to avoid those registers being overwritten in the callees.
> 
> Prior to commit 9012d011660e ("compiler: allow all arches to enable
> CONFIG_OPTIMIZE_INLINING"), the 'inline' marker was always enough for
> inlining functions, except on x86.
> 
> Since that commit, all architectures can enable CONFIG_OPTIMIZE_INLINING.
> So, __always_inline is now the only guaranteed way of forcible inlining.
> 
> I want to keep as much compiler's freedom as possible about the inlining
> decision. So, I changed the function call order instead of adding
> __always_inline around.
> 
> Call uaccess_save_and_enable() before assigning the __p ("r0"), and
> uaccess_restore() after evacuating the __e ("r0").
> 
> Fixes: 9012d011660e ("compiler: allow all arches to enable
> CONFIG_OPTIMIZE_INLINING")
> Reported-by: "kernelci.org bot" <bot@kernelci.org>
> Reported-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> ---

Thanks!

Tested-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>


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