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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>> _______________________________________________>> Containers mailing list>> Containers@lists.linux-foundation.org>> https://lists.linux-foundation.org/mailman/listinfo/containers>>> _______________________________________________> Containers mailing list> Containers@lists.linux-foundation.org> https://lists.linux-foundation.org/mailman/listinfo/containers>
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