jbd2: fix up sparse warnings in checkpoint code

Add missing __acquires() and __releases() annotations.  Also, in an
"this should never happen" WARN_ON check, if it *does* actually
happen, we need to release j_state_lock since this function is always
supposed to release that lock.  Otherwise, things will quickly grind
to a halt after the WARN_ON trips.

Fixes: 96f1e097 ("jbd2: avoid long hold times of j_state_lock...")
Cc: stable@kernel.org
Signed-off-by: NTheodore Ts'o <tytso@mit.edu>

fs/jbd2/checkpoint.c

@@ -106,6 +106,8 @@ static int __try_to_free_cp_buf(struct journal_head *jh)
  * for a checkpoint to free up some space in the log.
  */
 void __jbd2_log_wait_for_space(journal_t *journal)
+__acquires(&journal->j_state_lock)
+__releases(&journal->j_state_lock)
 {
 	int nblocks, space_left;
 	/* assert_spin_locked(&journal->j_state_lock); */

fs/jbd2/transaction.c

@@ -195,8 +195,10 @@ static void wait_transaction_switching(journal_t *journal)
 	DEFINE_WAIT(wait);
 
 	if (WARN_ON(!journal->j_running_transaction ||
-		    journal->j_running_transaction->t_state != T_SWITCH))
+		    journal->j_running_transaction->t_state != T_SWITCH)) {
+		read_unlock(&journal->j_state_lock);
 		return;
+	}
 	prepare_to_wait(&journal->j_wait_transaction_locked, &wait,
 			TASK_UNINTERRUPTIBLE);
 	read_unlock(&journal->j_state_lock);