From: Hugh Dickins hughd@google.com Subject: mm/huge_memory: fix lockdep complaint on 32-bit i_size_read()

Huge tmpfs testing, on 32-bit kernel with lockdep enabled, showed that __split_huge_page() was using i_size_read() while holding the irq-safe lru_lock and page tree lock, but the 32-bit i_size_read() uses an irq-unsafe seqlock which should not be nested inside them.

Instead, read the i_size earlier in split_huge_page_to_list(), and pass the end offset down to __split_huge_page(): all while holding head page lock, which is enough to prevent truncation of that extent before the page tree lock has been taken.

Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1811261520070.2275@eggly.anvils Fixes: baa355fd33142 ("thp: file pages support for split_huge_page()") Signed-off-by: Hugh Dickins hughd@google.com Acked-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: Jerome Glisse jglisse@redhat.com Cc: Konstantin Khlebnikov khlebnikov@yandex-team.ru Cc: Matthew Wilcox willy@infradead.org Cc: stable@vger.kernel.org [4.8+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/huge_memory.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-)

--- a/mm/huge_memory.c~mm-huge_memory-fix-lockdep-complaint-on-32-bit-i_size_read +++ a/mm/huge_memory.c @@ -2439,12 +2439,11 @@ static void __split_huge_page_tail(struc }

static void __split_huge_page(struct page *page, struct list_head *list, - unsigned long flags) + pgoff_t end, unsigned long flags) { struct page *head = compound_head(page); struct zone *zone = page_zone(head); struct lruvec *lruvec; - pgoff_t end = -1; int i;

lruvec = mem_cgroup_page_lruvec(head, zone->zone_pgdat); @@ -2452,9 +2451,6 @@ static void __split_huge_page(struct pag /* complete memcg works before add pages to LRU */ mem_cgroup_split_huge_fixup(head);

- if (!PageAnon(page)) - end = DIV_ROUND_UP(i_size_read(head->mapping->host), PAGE_SIZE); - for (i = HPAGE_PMD_NR - 1; i >= 1; i--) { __split_huge_page_tail(head, i, lruvec, list); /* Some pages can be beyond i_size: drop them from page cache */ @@ -2626,6 +2622,7 @@ int split_huge_page_to_list(struct page int count, mapcount, extra_pins, ret; bool mlocked; unsigned long flags; + pgoff_t end;

VM_BUG_ON_PAGE(is_huge_zero_page(page), page); VM_BUG_ON_PAGE(!PageLocked(page), page); @@ -2648,6 +2645,7 @@ int split_huge_page_to_list(struct page ret = -EBUSY; goto out; } + end = -1; mapping = NULL; anon_vma_lock_write(anon_vma); } else { @@ -2661,6 +2659,15 @@ int split_huge_page_to_list(struct page

anon_vma = NULL; i_mmap_lock_read(mapping); + + /* + *__split_huge_page() may need to trim off pages beyond EOF: + * but on 32-bit, i_size_read() takes an irq-unsafe seqlock, + * which cannot be nested inside the page tree lock. So note + * end now: i_size itself may be changed at any moment, but + * head page lock is good enough to serialize the trimming. + */ + end = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE); }

/* @@ -2707,7 +2714,7 @@ int split_huge_page_to_list(struct page if (mapping) __dec_node_page_state(page, NR_SHMEM_THPS); spin_unlock(&pgdata->split_queue_lock); - __split_huge_page(page, list, flags); + __split_huge_page(page, list, end, flags); if (PageSwapCache(head)) { swp_entry_t entry = { .val = page_private(head) };

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