memfd: Use radix_tree_deref_slot_protected to avoid the warning.

The commit 3ce6b467b9b2 ("memfd: Fix locking when tagging pins")
introduces the following warning messages.

*WARNING: suspicious RCU usage in memfd_wait_for_pins*

It is because we still use radix_tree_deref_slot without read_rcu_lock.
We should use radix_tree_deref_slot_protected instead in the case.

Cc: stable@vger.kernel.org
Fixes: 3ce6b467b9b2 ("memfd: Fix locking when tagging pins")
Signed-off-by: zhong jiang <zhongjiang@huawei.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/mm/shmem.c b/mm/shmem.c
index ac8a5fedc24542c4f95dfdae8495a80044c13d55..6266a7d1ba00cce52181f06f990822a30a12d519 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2464,7 +2464,7 @@ static void shmem_tag_pins(struct address_space *mapping)
 
        spin_lock_irq(&mapping->tree_lock);
        radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
-               page = radix_tree_deref_slot(slot);
+               page = radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
                if (!page || radix_tree_exception(page)) {
                        if (radix_tree_deref_retry(page)) {
                                slot = radix_tree_iter_retry(&iter);