Messages in this thread | | | Date | Fri, 18 Nov 2011 23:23:12 +0800 | Subject | Re: [PATCH] hugetlb: detect race if fail to COW | From | Hillf Danton <> |
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On Fri, Nov 18, 2011 at 11:07 PM, Michal Hocko <mhocko@suse.cz> wrote: > On Fri 18-11-11 22:04:37, Hillf Danton wrote: >> In the error path that we fail to allocate new huge page, before try again, we >> have to check race since page_table_lock is re-acquired. > > I do not think we can race here because we are serialized by > hugetlb_instantiation_mutex AFAIU. Without this lock, however, we could > fall into avoidcopy and shortcut despite the fact that other thread has > already did the job. > > The mutex usage is not obvious in hugetlb_cow so maybe we want to be > explicit about it (either a comment or do the recheck). >
Then the following check is unnecessary, no?
Thanks, Hillf
/* * Retake the page_table_lock to check for racing updates * before the page tables are altered */ spin_lock(&mm->page_table_lock); ptep = huge_pte_offset(mm, address & huge_page_mask(h)); if (likely(pte_same(huge_ptep_get(ptep), pte))) { /* Break COW */
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