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Date:   Wed, 15 Jan 2020 09:27:07 -0800
From:   Yang Shi <yang.shi@...ux.alibaba.com>
To:     Li Xinhai <lixinhai.lxh@...il.com>,
        akpm <akpm@...ux-foundation.org>
Cc:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: mempolicy: use VM_BUG_ON_VMA in
 queue_pages_test_walk()



On 1/15/20 4:08 AM, Li Xinhai wrote:
> On 2020-01-15 at 14:09 Yang Shi wrote:
>> The VM_BUG_ON() is already used by queue_pages_test_walk(), it sounds
>> better to dump more debug information by using VM_BUG_ON_VMA() to help
>> debugging.
>>
>> Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>
> The .test_walk() is to be called from pagewalk with the rule that 'start'
> and 'end' must within range of vma, in case the rule is broke, we detect
> it. This is not quite relevant to a bug of particular vma.

But when you run into VMA range check failure, isn't it helpful to dump 
the VMA range information to ease debugging? And, VM_BUG_ON is already 
used in the code, I'm supposed the users may prefer more debug 
information dumped for debug kernel.

>
>> ---
>> mm/mempolicy.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
>> index 067cf7d..801d45d 100644
>> --- a/mm/mempolicy.c
>> +++ b/mm/mempolicy.c
>> @@ -621,7 +621,7 @@ static int queue_pages_test_walk(unsigned long start, unsigned long end,
>> unsigned long flags = qp->flags;
>>
>> /* range check first */
>> -	VM_BUG_ON((vma->vm_start > start) || (vma->vm_end < end));
>> +	VM_BUG_ON_VMA((vma->vm_start > start) || (vma->vm_end < end), vma);
>>
>> if (!qp->first) {
>> qp->first = vma;
>> --
>> 1.8.3.1
>>
> >

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