jbd2: wake up journal waiters in FIFO order, not LIFO

commit 34fc876 upstream.

LIFO wakeup order is unfair and sometimes leads to a journal
user not being able to get a journal handle for hundreds of
transactions in a row.

FIFO wakeup can make things more fair.

Cc: [email protected]
Signed-off-by: Alexey Lyashkov <[email protected]>
Reviewed-by: Ritesh Harjani (IBM) <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Theodore Ts'o <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: pandafromspace

fs/jbd2/commit.c

@@ -581,7 +581,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
 	journal->j_running_transaction = NULL;
 	start_time = ktime_get();
 	commit_transaction->t_log_start = journal->j_head;
-	wake_up(&journal->j_wait_transaction_locked);
+	wake_up_all(&journal->j_wait_transaction_locked);
 	write_unlock(&journal->j_state_lock);
 
 	jbd_debug(3, "JBD2: commit phase 2a\n");

fs/jbd2/transaction.c

@@ -173,7 +173,7 @@ static void wait_transaction_locked(journal_t *journal)
 	int need_to_start;
 	tid_t tid = journal->j_running_transaction->t_tid;
 
-	prepare_to_wait(&journal->j_wait_transaction_locked, &wait,
+	prepare_to_wait_exclusive(&journal->j_wait_transaction_locked, &wait,
 			TASK_UNINTERRUPTIBLE);
 	need_to_start = !tid_geq(journal->j_commit_request, tid);
 	read_unlock(&journal->j_state_lock);
@@ -199,7 +199,7 @@ static void wait_transaction_switching(journal_t *journal)
 		read_unlock(&journal->j_state_lock);
 		return;
 	}
-	prepare_to_wait(&journal->j_wait_transaction_locked, &wait,
+	prepare_to_wait_exclusive(&journal->j_wait_transaction_locked, &wait,
 			TASK_UNINTERRUPTIBLE);
 	read_unlock(&journal->j_state_lock);
 	/*
@@ -911,7 +911,7 @@ void jbd2_journal_unlock_updates (journal_t *journal)
 	write_lock(&journal->j_state_lock);
 	--journal->j_barrier_count;
 	write_unlock(&journal->j_state_lock);
-	wake_up(&journal->j_wait_transaction_locked);
+	wake_up_all(&journal->j_wait_transaction_locked);
 }
 
 static void warn_dirty_buffer(struct buffer_head *bh)