Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH] mm: mempolicy: use VM_BUG_ON_VMA in
 queue_pages_test_walk()
To:     Li Xinhai <lixinhai.lxh@gmail.com>,
        akpm <akpm@linux-foundation.org>
Cc:     "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <1579068565-110432-1-git-send-email-yang.shi@linux.alibaba.com>
 <2020011520081970082765@gmail.com>
From:   Yang Shi <yang.shi@linux.alibaba.com>
Message-ID: <2a9ad6d6-af98-987a-0878-6058702db912@linux.alibaba.com>
Date:   Wed, 15 Jan 2020 09:27:07 -0800
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0)
 Gecko/20100101 Thunderbird/52.7.0
MIME-Version: 1.0
In-Reply-To: <2020011520081970082765@gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
Content-Language: en-US
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


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@linux.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
>>
> >