After fixing the race in follow_page(FOLL_GET) for hugepages, I start to observe the BUG of "get_page() on refcount 0 page" in hugetlb_fault() in the same test.
I'm not exactly sure about how this race is triggered, but hugetlb_fault() calls pte_page() and get_page() outside page table lock, so it's not safe. This patch checks the refcount of the gotten page, and aborts the page fault if the refcount is 0, expecting to retry. Signed-off-by: Naoya Horiguchi <[email protected]> Cc: <[email protected]> # [3.12+] --- mm/hugetlb.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git mmotm-2014-07-22-15-58.orig/mm/hugetlb.c mmotm-2014-07-22-15-58/mm/hugetlb.c index 6793914b6aac..86e7341aad77 100644 --- mmotm-2014-07-22-15-58.orig/mm/hugetlb.c +++ mmotm-2014-07-22-15-58/mm/hugetlb.c @@ -3189,7 +3189,8 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, * so no worry about deadlock. */ page = pte_page(entry); - get_page(page); + if (!get_page_unless_zero(page)) + goto out_put_pagecache; if (page != pagecache_page) lock_page(page); @@ -3215,15 +3216,14 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, out_ptl: spin_unlock(ptl); - + if (page != pagecache_page) + unlock_page(page); + put_page(page); +out_put_pagecache: if (pagecache_page) { unlock_page(pagecache_page); put_page(pagecache_page); } - if (page != pagecache_page) - unlock_page(page); - put_page(page); - out_mutex: mutex_unlock(&htlb_fault_mutex_table[hash]); return ret; -- 1.9.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
