ARM: fix __get_user_check() in case uaccess_* calls are not inlined

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>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Tested-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Tested-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>

0 files changed, 0 insertions, 0 deletions