Updated locking documentation for transaction_t

We used LockDoc to derive locking rules for each member
of struct transaction_t.
Based on those results, we extended the existing documentation
by more members of struct transaction_t, and updated the existing
documentation.

Link: https://lore.kernel.org/r/10cfbef1-994c-c604-f8a6-b1042fcc622f@tu-dortmund.deSigned-off-by: Alexander Lochmann <alexander.lochmann@tu-dortmund.de>
Signed-off-by: Horst Schirmeier <horst.schirmeier@tu-dortmund.de>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

include/linux/jbd2.h

@@ -538,6 +538,7 @@ struct transaction_chp_stats_s {
  * The transaction keeps track of all of the buffers modified by a
  * running transaction, and all of the buffers committed but not yet
  * flushed to home for finished transactions.
+ * (Locking Documentation improved by LockDoc)
  */
 
 /*
@@ -658,12 +659,12 @@ struct transaction_s
 	unsigned long		t_start;
 
 	/*
-	 * When commit was requested
+	 * When commit was requested [j_state_lock]
 	 */
 	unsigned long		t_requested;
 
 	/*
-	 * Checkpointing stats [j_checkpoint_sem]
+	 * Checkpointing stats [j_list_lock]
 	 */
 	struct transaction_chp_stats_s t_chp_stats;