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

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Date:   Mon, 16 Apr 2018 17:39:07 +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 4/13/2018 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);
                 vb_free(mem, size);
                 return;
         }

         va = find_vmap_area(addr);
         BUG_ON(!va);
+       debug_check_no_locks_freed(va->va_start, (va->va_end - 
va->va_start));
         free_unmap_vmap_area(va);
  }
  EXPORT_SYMBOL(vm_unmap_ram);


> debug on locks without even finding the vmap_area first. But it is true
> that in both these functions the vmap_area gets freed eventually. Hence
> the entire mapping [va->va_start --> va->va_end] gets unmapped. Sounds
> like these debug functions should have the entire range as argument.
> But I am not sure and will seek Michal's input on this.
> 

Chintan
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