[PATCH v2 2/4] ext4: fix incorrect tid assumption in __jbd2_log_wait_for_space()

[Luis Henriques (SUSE)]

Function __jbd2_log_wait_for_space() assumes that '0' is not a valid value
for transaction IDs, which is incorrect.  Don't assume that and invoke
jbd2_log_wait_commit() if the journal had a committing transaction instead.

Signed-off-by: Luis Henriques (SUSE) <luis.henriques@xxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
---
 fs/jbd2/checkpoint.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
index 951f78634adf..77bc522e6821 100644
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -79,9 +79,12 @@ __releases(&journal->j_state_lock)
 		if (space_left < nblocks) {
 			int chkpt = journal->j_checkpoint_transactions != NULL;
 			tid_t tid = 0;
+			bool has_transaction = false;
 
-			if (journal->j_committing_transaction)
+			if (journal->j_committing_transaction) {
 				tid = journal->j_committing_transaction->t_tid;
+				has_transaction = true;
+			}
 			spin_unlock(&journal->j_list_lock);
 			write_unlock(&journal->j_state_lock);
 			if (chkpt) {
@@ -89,7 +92,7 @@ __releases(&journal->j_state_lock)
 			} else if (jbd2_cleanup_journal_tail(journal) == 0) {
 				/* We were able to recover space; yay! */
 				;
-			} else if (tid) {
+			} else if (has_transaction) {
 				/*
 				 * jbd2_journal_commit_transaction() may want
 				 * to take the checkpoint_mutex if JBD2_FLUSHED