Re: [PATCH v2] ARM: add __always_inline to functions called from __get_user_check()

From: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
To: Masahiro Yamada <yamada.masahiro@socionext.com>,
	linux-arm-kernel@lists.infradead.org,
	Russell King <rmk+kernel@armlinux.org.uk>
Cc: Kate Stewart <kstewart@linuxfoundation.org>,
	Arnd Bergmann <arnd@arndb.de>, Enrico Weigelt <info@metux.net>,
	Vincent Whitchurch <vincent.whitchurch@axis.com>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Russell King <linux@armlinux.org.uk>,
	Stefan Agner <stefan@agner.ch>,
	linux-kernel@vger.kernel.org,
	Allison Randal <allison@lohutok.net>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Olof Johansson <olof@lixom.net>,
	Thomas Gleixner <tglx@linutronix.de>,
	Julien Thierry <julien.thierry.kdev@gmail.com>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH v2] ARM: add __always_inline to functions called from __get_user_check()
Date: Tue, 01 Oct 2019 11:03:40 +0200	[thread overview]
Message-ID: <196a63271591fbe0bc1fdd5a1a01a25caf5178d0.camel@suse.de> (raw)
In-Reply-To: <20191001083701.27207-1-yamada.masahiro@socionext.com>

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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@kernelci.org>
> Reported-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

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


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