Hi Michal,
On Wed, Mar 29, 2017 at 3:43 AM, Michal Hocko <mho...@kernel.org> wrote:
> On Wed 29-03-17 09:23:32, Vaneet Narang wrote:
>> Hi,
>>
>> >> Hmm, how can you track _all_ vmalloc allocations done on behalf of the
>> >> module? It is quite some time since I've checked kernel/module.c but
>> >> from my vague understading your check is basically only about statically
>> >> vmalloced areas by module loader. Is that correct? If yes then is this
>> >> actually useful? Were there any bugs in the loader code recently? What
>> >> led you to prepare this patch? All this should be part of the changelog!
>>
>> First of all there is no issue in kernel/module.c. This patch add
>> functionality
>> to detect scenario where some kernel module does some memory allocation but
>> gets
>> unloaded without doing vfree. For example
>> static int kernel_init(void)
>> {
>> char * ptr = vmalloc(400 * 1024);
>> return 0;
>> }
>
> How can you track that allocation back to the module? Does this patch
> actually works at all? Also why would be vmalloc more important than
> kmalloc allocations?
Doesn't the patch use caller's (in this case, the module is the
caller) text address for tracking this? vma->vm->caller should track
the caller doing the allocation?
>From the code:
vmalloc -> __vmalloc_node_flags
In __vmalloc_node_flags:
return __vmalloc_node(size, 1, flags, PAGE_KERNEL,
node, __builtin_return_address(0));
Since __vmalloc_node_flags is marked as inline, I believe the
__builtin_return_address(0) will return the return address of the
original vmalloc() call which is in the module calling vmalloc.
Regards,
Joel
