Vaidyanathan Srinivasan wrote:
>
> YAMAMOTO Takashi wrote:
>>> +unsigned long mem_container_isolate_pages(unsigned long nr_to_scan,
>>> + struct list_head *dst,
>>> + unsigned long *scanned, int order,
>>> + int mode, struct zone *z,
>>> + struct mem_container *mem_cont,
>>> + int active)
>>> +{
>>> + unsigned long nr_taken = 0;
>>> + struct page *page;
>>> + unsigned long scan;
>>> + LIST_HEAD(mp_list);
>>> + struct list_head *src;
>>> + struct meta_page *mp;
>>> +
>>> + if (active)
>>> + src = &mem_cont->active_list;
>>> + else
>>> + src = &mem_cont->inactive_list;
>>> +
>>> + for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
>>> + mp = list_entry(src->prev, struct meta_page, lru);
>> what prevents another thread from freeing mp here?
>
> mem_cont->lru_lock protects the list and validity of mp. If we hold
> mem_cont->lru_lock for this entire loop, then we preserve the validity
> of mp. However that will be holding up container charge and uncharge.
>
> This entire routing is called with zone->lru_lock held by the caller.
> So within a zone, this routine is serialized.
>
> However page uncharge may race with isolate page. But will that lead
> to any corruption of the list? We may be holding the lock for too
> much time just to be on the safe side.
>
> Please allow us some time to verify whether this is indeed inadequate
> locking that will lead to corruption of the list.
I did few runs and checked for ref_cnt on meta_page and there seems to
be a race between isolate pages and uncharge. We will probably have
to increase the ref_cnt on meta_page while we are isolating it. I am
trying to see if we can solve the problem by manipulating the ref_cnt
on the meta_page.
--Vaidy
> Thanks for pointing out this situation.
> --Vaidy
>
>>> + spin_lock(&mem_cont->lru_lock);
>>> + if (mp)
>>> + page = mp->page;
>>> + spin_unlock(&mem_cont->lru_lock);
>>> + if (!mp)
>>> + continue;
>> YAMAMOTO Takashi
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