hulk inclusion category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/IBDF90

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While we split/merge page in dynamic pool, the refcount of page may be increased to 1 due to prep_new_page(), and we then set the refcount to 0. That means there's a time window that the refcount of the free page is not 0.

split_huge_pages_set() will scan all pages and try to get the refcount If try to get refcount in the above time window and put_page() after the refcount is set to 0, the refcount will be decreased to -1.

It's dangerous if the refcount for page is not 0 when split/merge, so try not to get refcount there.

Fixes: 0bc0d0d57eda ("dhugetlb: backport dynamic hugetlb feature") Signed-off-by: Liu Shixin liushixin2@huawei.com --- mm/hugetlb.c | 4 ++-- mm/internal.h | 4 ++++ mm/page_alloc.c | 26 ++++++++++++++++++++++++++ 3 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 82a758bb8ac9..191ed8a6b0d0 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -3575,8 +3575,8 @@ static void add_new_huge_page_to_pool(struct dhugetlb_pool *hpool, list_add_tail(&page->lru, &hpool->dhugetlb_1G_freelists); hpool->free_unreserved_1G++; } else { - prep_new_page(page, PMD_SHIFT - PAGE_SHIFT, __GFP_COMP, 0); - set_page_count(page, 0); + prep_new_frozen_free_page(page, PMD_SHIFT - PAGE_SHIFT, + __GFP_COMP); list_add_tail(&page->lru, &hpool->dhugetlb_2M_freelists); hpool->free_unreserved_2M++; } diff --git a/mm/internal.h b/mm/internal.h index 72f77379b58f..e50363ddb416 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -185,6 +185,10 @@ extern void prep_compound_page(struct page *page, unsigned int order); extern int check_new_page(struct page *page); extern void post_alloc_hook(struct page *page, unsigned int order, gfp_t gfp_flags); +#ifdef CONFIG_DYNAMIC_HUGETLB +extern void prep_new_frozen_free_page(struct page *page, unsigned int order, + gfp_t gfp_flags); +#endif extern int user_min_free_kbytes;

#if defined CONFIG_COMPACTION || defined CONFIG_CMA diff --git a/mm/page_alloc.c b/mm/page_alloc.c index e2360fe3616d..787bbabc29d0 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2100,6 +2100,32 @@ void prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags, clear_page_pfmemalloc(page); }

+#ifdef CONFIG_DYNAMIC_HUGETLB +/* Similar with prep_new_page without set refcount to 1 */ +void prep_new_frozen_free_page(struct page *page, unsigned int order, + gfp_t gfp_flags) +{ + int i; + + set_page_private(page, 0); + + arch_alloc_page(page, order); + kernel_map_pages(page, 1 << order, 1); + kasan_alloc_pages(page, order); + kernel_poison_pages(page, 1 << order, 1); + set_page_owner(page, order, gfp_flags); + + if (!free_pages_prezeroed() && (gfp_flags & __GFP_ZERO)) + for (i = 0; i < (1 << order); i++) + clear_highpage(page + i); + + if (order && (gfp_flags & __GFP_COMP)) + prep_compound_page(page, order); + + clear_page_pfmemalloc(page); +} +#endif + /* * Go through the free lists for the given migratetype and remove * the smallest available page from the freelists