reiserfs: don't use congestion_wait()

Block devices do not, in general, report congestion any more, so this
congestion_wait() is effectively just a sleep.

It isn't entirely clear what is being waited for, but as we only wait
when j_async_throttle is elevated, it seems reasonable to stop waiting
when j_async_throttle becomes zero - or after the same timeout.

So change to use wait_event_event_timeout() for waiting, and
wake_up_var() to signal an end to waiting.

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: NeilBrown <[e-mail]>
Signed-off-by: Jan Kara <[e-mail]>

fs/reiserfs/journal.c

···
 		int depth;
 
 		depth = reiserfs_write_unlock_nested(s);
-		congestion_wait(BLK_RW_ASYNC, HZ / 10);
+		wait_var_event_timeout(&j->j_async_throttle,
+				       atomic_read(&j->j_async_throttle) == 0,
+				       HZ / 10);
 		reiserfs_write_lock_nested(s, depth);
 	}
 
···
 			put_bh(tbh) ;
 		}
 	}
-	atomic_dec(&journal->j_async_throttle);
+	if (atomic_dec_and_test(&journal->j_async_throttle))
+		wake_up_var(&journal->j_async_throttle);
 
 	for (i = 0; i < (jl->j_len + 1); i++) {
 		bn = SB_ONDISK_JOURNAL_1st_BLOCK(s) +