Re: [patch 3/3] IA64: virt_to_page() can be called with NULL arg

[Kirill Korotaev <dev@sw.ru>]

Jes Sorensen wrote:
> Kirill Korotaev wrote:
> 
>>>>>>>>"akpm" = akpm  <akpm@osdl.org> writes:
>>>
>>>akpm> From: Kirill Korotaev <dev@openvz.org> It does not return NULL
>>>akpm> when arg is NULL.
>>>
>>>Shouldn't the real fix be to track down who calls virt_to_page() with
>>>a NULL pointer? IMHO it is bogus to do so.
>>
>>what do you propose? to insert BUG_ON(!kaddr) into virt_to_page()?
>>in this case caller in question should be still fixed.
> 
> 
> If you hit this, yes I'd insert the BUG_ON in your test kernel and fix
> the code. Maybe add the BUG_ON in upstream for CONFIG_DEBUG or
> something.
I guess then all the platforms should be analyzed/patched carefully
or all the callers of virt_to_page().
Care to create debug patch?

> Which callers did you see cause this? If it was a common problem I would
> expect a lot of data corruption or crashes on ia64 systems which I
> haven't heard of.
from the patch:
pte_alloc_one() calls pgtable_quicklist_alloc() which can return NULL in
case of allocation failure.

It was hit on OpenVZ where kernel memory is accounted and limited on
per-container basis (it is possible to DoS using page tables allocations).
In mainstream the bug can be hit if OOM killer
kills the process and __get_free_page() returns NULL which is rare, but still possible.

Thanks,
Kirill