Re: [discuss] mmap, mbind and write to mmap'ed memory crashes 2.6.16-rc1[2] on 2 node X86_64

[Bharata B Rao <bharata@in.ibm.com>]

On Wed, Feb 15, 2006 at 11:16:20AM +0530, Bharata B Rao wrote:
> On Tue, Feb 14, 2006 at 11:33:00AM -0800, Christoph Lameter wrote:
> > I just took another look at this issue and I cannot see anything wrong. An 
> > empty zone should be ignored by the page allocator since nr_free == 0. My 
> > patch should not be needed.
> 
> There is a check for list_empty(&area->free_list) in __rmqueue(), which
> I think is one of the points in the page allocator where the emptiness of
> the free_area list is checked. The current zone(when the crash happens)
> bypasses this test leading to this crash.
> 

We don't initialize the free_area list for all zones. Instead,
free_area_init_core() does that only for zones which are non-empty.

But in __rmqueue(), we depend on these free_area lists to be intialized
correctly for all zones, which is not true in the present case we
are discussing.

I think we either need to initialize free_area lists for all zones
or check for !zone->free_area->nr_free in __rmqueue().

Even with this, mbind still needs to be fixed. Even though it
can't get a conforming zone in the node (MPOL_BIND case), right now,
it goes ahead with the "bind"ing of the memory area. This causes the
application to crash (assuming we have fixed the __rmqueue kernel crash)
(Haven't yet figured our why exactly the application dies)

Regards,
Bharata.