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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>,
        Anshuman Khandual <Anshuman.Khandual@arm.com>
Cc:     linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
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From:   Christophe Leroy <christophe.leroy@c-s.fr>
Message-ID: <3cfec421-4006-4159-ca32-313ff5196ff9@c-s.fr>
Date:   Fri, 25 Oct 2019 09:11:12 +0200
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Le 25/10/2019 à 07:52, Qian Cai a écrit :
> 
> 
>> 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
> 

Are we talking about this peace of code ?

+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) ||
+		(random_vaddr < FIRST_USER_ADDRESS));
+	return random_vaddr;
+}
+

ramdom_vaddr is unsigned,
random_pages is unsigned and lower than total_user_pages

So the max value random_vaddr can get is FIRST_USER_ADDRESS + 
((TASK_SIZE - FIRST_USER_ADDRESS - 1) / PAGE_SIZE) * PAGE_SIZE = 
TASK_SIZE - 1
And the min value random_vaddr can get is FIRST_USER_ADDRESS (that's 
when random_pages = 0)

So the WARN_ON() is just unneeded, isn't it ?

Christophe