Re: [PATCH V6 2/2] mm/debug: Add tests validating architecture page table helpers

From: Qian Cai <cai@lca•pw>
To: Anshuman Khandual <anshuman.khandual@arm•com>, linux-mm@kvack•org
Cc: Mark Rutland <mark.rutland@arm•com>,
	linux-ia64@vger•kernel.org, linux-sh@vger•kernel.org,
	Peter Zijlstra <peterz@infradead•org>,
	James Hogan <jhogan@kernel•org>,
	Heiko Carstens <heiko.carstens@de•ibm.com>,
	Michal Hocko <mhocko@kernel•org>,
	Dave Hansen <dave.hansen@intel•com>,
	Paul Mackerras <paulus@samba•org>,
	sparclinux@vger•kernel.org, Thomas Gleixner <tglx@linutronix•de>,
	linux-s390@vger•kernel.org, Jason Gunthorpe <jgg@ziepe•ca>,
	Michael Ellerman <mpe@ellerman•id.au>,
	x86@kernel•org, Russell King - ARM Linux <linux@armlinux•org.uk>,
	Matthew Wilcox <willy@infradead•org>,
	Steven Price <Steven.Price@arm•com>,
	Tetsuo Handa <penguin-kernel@i-love•sakura.ne.jp>,
	Gerald Schaefer <gerald.schaefer@de•ibm.com>,
	linux-snps-arc@lists•infradead.org,
	linux-arm-kernel@lists•infradead.org,
	Kees Cook <keescook@chromium•org>,
	Masahiro Yamada <yamada.masahiro@socionext•com>,
	Mark Brown <broonie@kernel•org>,
	"Kirill A . Shutemov" <kirill@shutemov•name>,
	Dan Williams <dan.j.williams@intel•com>,
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	linux-kernel@vger•kernel.org, Paul Burton <paul.burton@mips•com>,
	Mike Rapoport <rppt@linux•vnet.ibm.com>,
	Vineet Gupta <vgupta@synopsys•com>,
	Martin Schwidefsky <schwidefsky@de•ibm.com>,
	Andrew Morton <akpm@linux-foundation•org>,
	linuxppc-dev@lists•ozlabs.org,
	"David S. Miller" <davem@davemloft•net>
Subject: Re: [PATCH V6 2/2] mm/debug: Add tests validating architecture page table helpers
Date: Tue, 15 Oct 2019 14:09:42 -0400	[thread overview]
Message-ID: <1571162982.5937.42.camel@lca.pw> (raw)
In-Reply-To: <1571131302-32290-3-git-send-email-anshuman.khandual@arm.com>

On Tue, 2019-10-15 at 14:51 +0530, Anshuman Khandual wrote:
> +static unsigned long __init get_random_vaddr(void)
> +{
> +	unsigned long random_vaddr, random_pages, total_user_pages;
> +
> +	total_user_pages = (TASK_SIZE - FIRST_USER_ADDRESS) / PAGE_SIZE;
> +
> +	random_pages = get_random_long() % total_user_pages;
> +	random_vaddr = FIRST_USER_ADDRESS + random_pages * PAGE_SIZE;
> +
> +	WARN_ON(random_vaddr > TASK_SIZE);
> +	WARN_ON(random_vaddr < FIRST_USER_ADDRESS);

It would be nice if this patch does not introduce a new W=1 GCC warning here on
x86 because FIRST_USER_ADDRESS is 0, and GCC think the code is dumb because
"random_vaddr" is unsigned,

In file included from ./arch/x86/include/asm/bug.h:83,
                 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:359:23: warning: comparison of unsigned expression < 0 is
always false [-Wtype-limits]
  WARN_ON(random_vaddr < FIRST_USER_ADDRESS);
                       ^
./include/asm-generic/bug.h:113:25: note: in definition of macro ‘WARN_ON’
  int __ret_warn_on = !!(condition);    \
                         ^~~~~~~~~

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