1 files changed, 13 insertions, 13 deletions
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 148ef08f19dd..28642c188c93 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1238,16 +1238,15 @@ static unsigned char __swap_entry_free_locked(struct swap_info_struct *p,
 
 /*
  * When we get a swap entry, if there aren't some other ways to
- * prevent swapoff, such as the folio in swap cache is locked, page
- * table lock is held, etc., the swap entry may become invalid because
- * of swapoff.  Then, we need to enclose all swap related functions
- * with get_swap_device() and put_swap_device(), unless the swap
- * functions call get/put_swap_device() by themselves.
+ * prevent swapoff, such as the folio in swap cache is locked, RCU
+ * reader side is locked, etc., the swap entry may become invalid
+ * because of swapoff.  Then, we need to enclose all swap related
+ * functions with get_swap_device() and put_swap_device(), unless the
+ * swap functions call get/put_swap_device() by themselves.
  *
- * Note that when only holding the PTL, swapoff might succeed immediately
- * after freeing a swap entry. Therefore, immediately after
- * __swap_entry_free(), the swap info might become stale and should not
- * be touched without a prior get_swap_device().
+ * RCU reader side lock (including any spinlock) is sufficient to
+ * prevent swapoff, because synchronize_rcu() is called in swapoff()
+ * before freeing data structures.
  *
  * Check whether swap entry is valid in the swap device.  If so,
  * return pointer to swap_info_struct, and keep the swap entry valid
@@ -2544,10 +2543,11 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 
 	/*
 	 * Wait for swap operations protected by get/put_swap_device()
-	 * to complete.
-	 *
-	 * We need synchronize_rcu() here to protect the accessing to
-	 * the swap cache data structure.
+	 * to complete.  Because of synchronize_rcu() here, all swap
+	 * operations protected by RCU reader side lock (including any
+	 * spinlock) will be waited too.  This makes it easy to
+	 * prevent folio_test_swapcache() and the following swap cache
+	 * operations from racing with swapoff.
 	 */
 	percpu_ref_kill(&p->users);
 	synchronize_rcu();