Re: [PATCH v2] mm: Fix slab->page _count corruption.

[Pravin Shelar <pshelar@nicira.com>]

On Mon, May 14, 2012 at 3:34 PM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> On Mon, 2012-05-14 at 15:29 -0700, Pravin B Shelar wrote:
>> On arches that do not support this_cpu_cmpxchg_double slab_lock is used
>> to do atomic cmpxchg() on double word which contains page->_count.
>> page count can be changed from get_page() or put_page() without taking
>> slab_lock. That corrupts page counter.
>>
>> Following patch fixes it by moving page->_count out of cmpxchg_double
>> data. So that slub does no change it while updating slub meta-data in
>> struct page.
>
> I say again : Page is owned by slub, so get_page() or put_page() is not
> allowed ?
>
This is already done in multiple subsystem in Linux kernel. e.g.
ocfs, xfs, etc.
So object from slab can be passed to IO using DMA. I don't think this
rule you referring to is enforced anywhere.

Thanks,
Pravin.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>