From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl1-f197.google.com (mail-pl1-f197.google.com [209.85.214.197]) by kanga.kvack.org (Postfix) with ESMTP id 975AF6B445A for ; Mon, 26 Nov 2018 18:22:02 -0500 (EST) Received: by mail-pl1-f197.google.com with SMTP id p3so2415831plk.9 for ; Mon, 26 Nov 2018 15:22:02 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id y73sor2781442pfd.54.2018.11.26.15.22.01 for (Google Transport Security); Mon, 26 Nov 2018 15:22:01 -0800 (PST) Date: Mon, 26 Nov 2018 15:21:58 -0800 (PST) From: Hugh Dickins Subject: [PATCH 03/10] mm/huge_memory: fix lockdep complaint on 32-bit i_size_read() In-Reply-To: Message-ID: References: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: "Kirill A. Shutemov" , "Kirill A. Shutemov" , Matthew Wilcox , linux-mm@kvack.org 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. Fixes: baa355fd33142 ("thp: file pages support for split_huge_page()") Signed-off-by: Hugh Dickins Cc: Kirill A. Shutemov Cc: stable@vger.kernel.org # 4.8+ --- mm/huge_memory.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index cef2c256e7c4..622cced74fd9 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2439,12 +2439,11 @@ static void __split_huge_page_tail(struct page *head, int tail, } 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 page *page, struct list_head *list, /* 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 *page, struct list_head *list) 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 *page, struct list_head *list) 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 *page, struct list_head *list) 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 *page, struct list_head *list) 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) }; -- 2.20.0.rc0.387.gc7a69e6b6c-goog