linux-kernel - Re: mm/gup.o: warning: objtool: faultin_page

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Message-ID: <c8db754f-57b0-4430-b22a-87f8f3758ce9@redhat.com>
Date: Tue, 23 Jul 2024 10:28:15 +0200
From: David Hildenbrand <david@...hat.com>
To: kernel test robot <lkp@...el.com>
Cc: oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
 Andrew Morton <akpm@...ux-foundation.org>,
 Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: mm/gup.o: warning: objtool: faultin_page_range+0x100: unreachable
 instruction

On 23.07.24 00:56, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   933069701c1b507825b514317d4edd5d3fd9d417
> commit: 631426ba1d45a8672b177ee85ad4cabe760dd131 mm/madvise: make MADV_POPULATE_(READ|WRITE) handle VM_FAULT_RETRY properly
> date:   3 months ago
> config: loongarch-randconfig-001-20240722 (https://download.01.org/0day-ci/archive/20240723/202407230630.3vGhnlFB-lkp@intel.com/config)
> compiler: loongarch64-linux-gcc (GCC) 14.1.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240723/202407230630.3vGhnlFB-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@...el.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202407230630.3vGhnlFB-lkp@intel.com/
> 
> All warnings (new ones prefixed by >>):
> 
>     mm/gup.o: warning: objtool: get_user_pages_remote+0x160: unreachable instruction
>     mm/gup.o: warning: objtool: get_user_pages+0x12c: unreachable instruction
>     mm/gup.o: warning: objtool: get_user_pages_unlocked+0x138: unreachable instruction
>     mm/gup.o: warning: objtool: __gup_longterm_locked+0x3d8: unreachable instruction
>>> mm/gup.o: warning: objtool: faultin_page_range+0x100: unreachable instruction
> 
> 
> objdump-func vmlinux.o faultin_page_range:
> 

I'm afraid I don't know how serious I should take this report :/

The commit is 3 month old and was found on some toolchain with some 
randconfig on some architecture, in code that is not particularly 
architecture specific.

I wish I could even understand from the report what is happening here 
("unreachable instruction" -- isn't that the compilers fault if it 
generates that such that objtool would complain? Why is that a C code 
issue?)

Please, someone shout if I should take a closer look at this.

-- 
Cheers,

David / dhildenb