linux-kernel - Re: [PATCH 2/2] mm: vmalloc: Pass proper vm

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Date:   Tue, 17 Apr 2018 10:40:57 +0530
From:   Chintan Pandya <cpandya@...eaurora.org>
To:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>, vbabka@...e.cz,
        labbott@...hat.com, catalin.marinas@....com, hannes@...xchg.org,
        f.fainelli@...il.com, xieyisheng1@...wei.com,
        ard.biesheuvel@...aro.org, richard.weiyang@...il.com,
        byungchul.park@....com
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm: vmalloc: Pass proper vm_start into debugobjects



On 4/17/2018 8:39 AM, Anshuman Khandual wrote:
> On 04/16/2018 05:39 PM, Chintan Pandya wrote:
>>
>>
>> On 4/13/2018 5:31 PM, Anshuman Khandual wrote:
>>> On 04/13/2018 05:03 PM, Chintan Pandya wrote:
>>>> Client can call vunmap with some intermediate 'addr'
>>>> which may not be the start of the VM area. Entire
>>>> unmap code works with vm->vm_start which is proper
>>>> but debug object API is called with 'addr'. This
>>>> could be a problem within debug objects.
>>>>
>>>> Pass proper start address into debug object API.
>>>>
>>>> Signed-off-by: Chintan Pandya <cpandya@...eaurora.org>
>>>> ---
>>>>    mm/vmalloc.c | 4 ++--
>>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
>>>> index 9ff21a1..28034c55 100644
>>>> --- a/mm/vmalloc.c
>>>> +++ b/mm/vmalloc.c
>>>> @@ -1526,8 +1526,8 @@ static void __vunmap(const void *addr, int
>>>> deallocate_pages)
>>>>            return;
>>>>        }
>>>>    -    debug_check_no_locks_freed(addr, get_vm_area_size(area));
>>>> -    debug_check_no_obj_freed(addr, get_vm_area_size(area));
>>>> +    debug_check_no_locks_freed(area->addr, get_vm_area_size(area));
>>>> +    debug_check_no_obj_freed(area->addr, get_vm_area_size(area));
>>>
>>> This kind of makes sense to me but I am not sure. We also have another
>>> instance of this inside the function vm_unmap_ram() where we call for
>> Right, I missed it. I plan to add below stub in v2.
>>
>> --- a/mm/vmalloc.c
>> +++ b/mm/vmalloc.c
>> @@ -1124,15 +1124,15 @@ void vm_unmap_ram(const void *mem, unsigned int
>> count)
>>          BUG_ON(addr > VMALLOC_END);
>>          BUG_ON(!PAGE_ALIGNED(addr));
>>
>> -       debug_check_no_locks_freed(mem, size);
>> -
>>          if (likely(count <= VMAP_MAX_ALLOC)) {
>> +               debug_check_no_locks_freed(mem, size);
> 
> It should have been 'va->va_start' instead of 'mem' in here but as
> said before it looks correct to me but I am not really sure.

vb_free() doesn't honor va->va_start. If mem is not va_start and
deliberate, one will provide proper size. And that should be okay
to do as per the code. So, I don't think this particular debug_check
should have passed va_start in args.

> 

Chintan
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