On Wed, 18 Jul 2012 11:04:09 +0530
"Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> wrote:
> From: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
>
> Since we cannot fail in hugetlb_cgroup_move_parent, we don't really
> need to check whether cgroup have any change left after that. Also skip
> those hstates for which we don't have any charge in this cgroup.
>
> ...
>
> + for_each_hstate(h) {
> + /*
> + * if we don't have any charge, skip this hstate
> + */
> + idx = hstate_index(h);
> + if (res_counter_read_u64(&h_cg->hugepage[idx], RES_USAGE) == 0)
> + continue;
> + spin_lock(&hugetlb_lock);
> + list_for_each_entry(page, &h->hugepage_activelist, lru)
> + hugetlb_cgroup_move_parent(idx, cgroup, page);
> + spin_unlock(&hugetlb_lock);
> + VM_BUG_ON(res_counter_read_u64(&h_cg->hugepage[idx], RES_USAGE));
> + }
> out:
> return ret;
> }
This looks fishy.
We test RES_USAGE before taking hugetlb_lock. What prevents some other
thread from increasing RES_USAGE after that test?
After walking the list we test RES_USAGE after dropping hugetlb_lock.
What prevents another thread from incrementing RES_USAGE before that
test, triggering the BUG?
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