linux-kernel - Re: [PATCH v2] ARM: add __always_inline to functions called from __get_user

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Date:   Tue, 01 Oct 2019 11:03:40 +0200
From:   Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        linux-arm-kernel@...ts.infradead.org,
        Russell King <rmk+kernel@...linux.org.uk>
Cc:     Kate Stewart <kstewart@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>, Enrico Weigelt <info@...ux.net>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Russell King <linux@...linux.org.uk>,
        Stefan Agner <stefan@...er.ch>, linux-kernel@...r.kernel.org,
        Allison Randal <allison@...utok.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Olof Johansson <olof@...om.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2] ARM: add __always_inline to functions called from
 __get_user_check()

On Tue, 2019-10-01 at 17:37 +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 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.
> Otherwise, those register assignments would be entirely dropped,
> according to my analysis of the disassembly.
> 
> 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 also added __always_inline to 4 functions in the call-graph from the
> __get_user_check() macro.
> 
> Fixes: 9012d011660e ("compiler: allow all arches to enable
> CONFIG_OPTIMIZE_INLINING")
> Reported-by: "kernelci.org bot" <bot@...nelci.org>
> Reported-by: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>

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


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