On Mon, Mar 05, 2012 at 05:42:56PM +0900, Namhyung Kim wrote:

2012-03-04 7:34 PM, Minchan Kim wrote:

quoted

Hi Namhyung,

Hi Minchan,
glad to see you here again :)

Thanks!

quoted

On Wed, Feb 29, 2012 at 05:54:34PM +0900, Namhyung Kim wrote:

quoted

Unlike SLAB, SLUB doesn't set PG_slab on tail pages, so if a user would
call free_pages() incorrectly on a object in a tail page, she will get
i confused with the undefined result. Setting the flag would help her by
emitting a warning on bad_page() in such a case.

Reported-by: Sangseok Lee <redacted>
Signed-off-by: Namhyung Kim <redacted>

I read this thread and I feel the we don't reach right point.
I think it's not a compound page problem.
We can face above problem where we allocates big order page without __GFP_COMP
and free middle page of it.

Fortunately, We can catch such a problem by put_page_testzero in __free_pages
if you enable CONFIG_DEBUG_VM.

Did you tried that with CONFIG_DEBUG_VM?

To be honest, I don't have a real test environment which brings this
issue in the first place. On my simple test environment, enabling
CONFIG_DEBUG_VM emits a bug when I tried to free middle of the slab
pages. Thanks for pointing it out.

However I guess there was a chance to bypass that test anyhow since
it did reach to __free_pages_ok(). If the page count was 0 already,
free_pages() will prevent it from getting to the function even
though CONFIG_DEBUG_VM was disabled. But I don't think it's a kernel
bug - it seems entirely our fault :( I'll recheck and talk about it
with my colleagues.

Let me ask a question.
Could you see bad page message by PG_slab with SLUB after you apply your patch?

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