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 <hughd@xxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # 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
