mm, hugetlb: fix huge_pte_alloc BUG_ON
Zhong Jiang has reported a BUG_ON from huge_pte_alloc hitting when he
runs his database load with memory online and offline running in
parallel. The reason is that huge_pmd_share might detect a shared pmd
which is currently migrated and so it has migration pte which is
!pte_huge.
There doesn't seem to be any easy way to prevent from the race and in
fact seeing the migration swap entry is not harmful. Both callers of
huge_pte_alloc are prepared to handle them. copy_hugetlb_page_range
will copy the swap entry and make it COW if needed. hugetlb_fault will
back off and so the page fault is retries if the page is still under
migration and waits for its completion in hugetlb_fault.
That means that the BUG_ON is wrong and we should update it. Let's
simply check that all present ptes are pte_huge instead.
Link: http://lkml.kernel.org/r/20160721074340.GA26398@dhcp22.suse.cz
Signed-off-by: Michal Hocko <mhocko@suse.com>
Reported-by: zhongjiang <zhongjiang@huawei.com>
Acked-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 file changed