linux-kernel - Re: [PATCH] s390/mm: Explicitly compare PAGE_DEFAULT_KEY against zero in storage_key_init

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Date:   Mon, 17 Feb 2020 18:07:33 +0100
From:   Vasily Gorbik <gor@...ux.ibm.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Heiko Carstens <heiko.carstens@...ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH] s390/mm: Explicitly compare PAGE_DEFAULT_KEY against
 zero in storage_key_init_range

On Thu, Feb 13, 2020 at 11:42:07PM -0700, Nathan Chancellor wrote:
> Clang warns:
> 
>  In file included from ../arch/s390/purgatory/purgatory.c:10:
>  In file included from ../include/linux/kexec.h:18:
>  In file included from ../include/linux/crash_core.h:6:
>  In file included from ../include/linux/elfcore.h:5:
>  In file included from ../include/linux/user.h:1:
>  In file included from ../arch/s390/include/asm/user.h:11:
>  ../arch/s390/include/asm/page.h:45:6: warning: converting the result of
>  '<<' to a boolean always evaluates to false
>  [-Wtautological-constant-compare]
>          if (PAGE_DEFAULT_KEY)
>             ^
>  ../arch/s390/include/asm/page.h:23:44: note: expanded from macro
>  'PAGE_DEFAULT_KEY'
>  #define PAGE_DEFAULT_KEY        (PAGE_DEFAULT_ACC << 4)
>                                                   ^
>  1 warning generated.
> 
> Explicitly compare this against zero to silence the warning as it is
> intended to be used in a boolean context.
> 
> Fixes: de3fa841e429 ("s390/mm: fix compile for PAGE_DEFAULT_KEY != 0")
> Link: https://github.com/ClangBuiltLinux/linux/issues/860
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
Applied to fixes, thanks