mm/huge_memory: fix lockdep complaint on 32-bit i_size_read()

PATCH New [email protected] 1 participant 1 message Dec 1, 2018

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Stable branch Memory management THP

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2018-12-01 09:21 UTC #0 lore raw

PATCH 23/31 mm/huge_memory: fix lockdep complaint on 32-bit i_size_read()

From: Hugh Dickins <[email protected]>
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/[email protected] open here

Fixes baa355fd33142 ("thp: file pages support for split_huge_page()")

Signed-off-by Hugh Dickins <[email protected]>

Acked-by Kirill A. Shutemov <[email protected]>

Cc Jerome Glisse <[email protected]>

Cc Konstantin Khlebnikov <[email protected]>

Cc Matthew Wilcox <[email protected]>

Cc <[email protected]> [4.8+]

Signed-off-by Andrew Morton <[email protected]>

---

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

mm/huge_memory.c renamed from mm/huge_memory.c~mm-huge_memory-fix-lockdep-complaint-on-32-bit-i_size_read +13 -6

@@ -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) };