Messages in this thread | | | From | Masahiro Yamada <> | Date | Mon, 30 Sep 2019 17:26:27 +0900 | Subject | Re: [PATCH] ARM: fix __get_user_check() in case uaccess_* calls are not inlined |
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Hi Arnd,
On Mon, Sep 30, 2019 at 4:57 PM Arnd Bergmann <arnd@arndb.de> wrote: > > On Mon, Sep 30, 2019 at 8:01 AM Masahiro Yamada > <yamada.masahiro@socionext.com> 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> > > Acked-by: Arnd Bergmann <arnd@arndb.de> > > The patch looks reasonable to me, but I think we should also revert > commit ac7c3e4ff401 ("compiler: enable CONFIG_OPTIMIZE_INLINING > forcibly") in mainline for now, as it caused this to happen all the time rather > than only for users that expliticly select CONFIG_OPTIMIZE_INLINING. > > We have had other bug reports starting with that commit that run into > similar issues, and I'm sure there are more of them. I don't mind having it > in linux-next for a while long, but I think it was premature to have it merged > into mainline. > > Arnd
Hmm, I know you are testing randconfig build tests, but how many people are testing the kernel boot in linux-next?
People and kernelci started to report the issue immediately after it landed in the mainline...
-- Best Regards Masahiro Yamada
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