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Subject: Re: [PATCH V7] mm/debug: Add tests validating architecture page table
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To:     Qian Cai <cai@lca.pw>
Cc:     linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
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From:   Anshuman Khandual <anshuman.khandual@arm.com>
Message-ID: <5ce5a76c-ea89-c2a1-6665-7d75bce5fb87@arm.com>
Date:   Fri, 25 Oct 2019 12:05:18 +0530
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On 10/25/2019 11:22 AM, Qian Cai wrote:
> 
> 
>> On Oct 24, 2019, at 11:45 PM, Anshuman Khandual <Anshuman.Khandual@arm.com> wrote:
>>
>> Nothing specific. But just tested this with x86 defconfig with relevant configs
>> which are required for this test. Not sure if it involved W=1.
> 
> No, it will not. It needs to run like,
> 
> make W=1 -j 64 2>/tmp/warns

Ahh, so we explicitly ask for it.

Unfortunately compiler still flags it as an warning. Just wondering why this
is still a problem if the second condition for an OR expression is always false.
Because evaluation still needs to be performed for the first condition anyways,
before arriving at the result.

  DESCEND  objtool
  CALL    scripts/atomic/check-atomics.sh
  CALL    scripts/checksyscalls.sh
  CHK     include/generated/compile.h
  CC      mm/debug_vm_pgtable.o
In file included from ./arch/x86/include/asm/bug.h:83:0,
                 from ./include/linux/bug.h:5,
                 from ./include/linux/mmdebug.h:5,
                 from ./include/linux/gfp.h:5,
                 from mm/debug_vm_pgtable.c:13:
mm/debug_vm_pgtable.c: In function ‘get_random_vaddr’:
mm/debug_vm_pgtable.c:314:17: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits]
   (random_vaddr < FIRST_USER_ADDRESS));
                 ^
./include/asm-generic/bug.h:113:25: note: in definition of macro ‘WARN_ON’
  int __ret_warn_on = !!(condition);    \
                         ^~~~~~~~~

As you mentioned GCC is quite stubborn here. Anyways, lets keep it unchanged.