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-rw-r--r--include/linux/radix-tree.h16
-rw-r--r--mm/migrate.c4
2 files changed, 18 insertions, 2 deletions
diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index ab2baa5..23241c2 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -146,6 +146,22 @@ static inline void *radix_tree_deref_slot(void **pslot)
}
/**
+ * radix_tree_deref_slot_protected - dereference a slot without RCU lock but with tree lock held
+ * @pslot: pointer to slot, returned by radix_tree_lookup_slot
+ * Returns: item that was stored in that slot with any direct pointer flag
+ * removed.
+ *
+ * Similar to radix_tree_deref_slot but only used during migration when a pages
+ * mapping is being moved. The caller does not hold the RCU read lock but it
+ * must hold the tree lock to prevent parallel updates.
+ */
+static inline void *radix_tree_deref_slot_protected(void **pslot,
+ spinlock_t *treelock)
+{
+ return rcu_dereference_protected(*pslot, lockdep_is_held(treelock));
+}
+
+/**
* radix_tree_deref_retry - check radix_tree_deref_slot
* @arg: pointer returned by radix_tree_deref_slot
* Returns: 0 if retry is not required, otherwise retry is required
diff --git a/mm/migrate.c b/mm/migrate.c
index 1a531b7..89a6bc8 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -248,7 +248,7 @@ static int migrate_page_move_mapping(struct address_space *mapping,
expected_count = 2 + page_has_private(page);
if (page_count(page) != expected_count ||
- (struct page *)radix_tree_deref_slot(pslot) != page) {
+ radix_tree_deref_slot_protected(pslot, &mapping->tree_lock) != page) {
spin_unlock_irq(&mapping->tree_lock);
return -EAGAIN;
}
@@ -320,7 +320,7 @@ int migrate_huge_page_move_mapping(struct address_space *mapping,
expected_count = 2 + page_has_private(page);
if (page_count(page) != expected_count ||
- (struct page *)radix_tree_deref_slot(pslot) != page) {
+ radix_tree_deref_slot_protected(pslot, &mapping->tree_lock) != page) {
spin_unlock_irq(&mapping->tree_lock);
return -EAGAIN;
}
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