ext4: fix incorrect tid assumption in ext4_wait_for_tail_page_commit()

commit dd589b0 upstream.

Function ext4_wait_for_tail_page_commit() 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@linux.dev>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20240724161119.13448-2-luis.henriques@linux.dev
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Luis Henriques (SUSE)

fs/ext4/inode.c

@@ -5257,8 +5257,9 @@ static void ext4_wait_for_tail_page_commit(struct inode *inode)
 {
 	unsigned offset;
 	journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
-	tid_t commit_tid = 0;
+	tid_t commit_tid;
 	int ret;
+	bool has_transaction;
 
 	offset = inode->i_size & (PAGE_SIZE - 1);
 	/*
@@ -5283,12 +5284,14 @@ static void ext4_wait_for_tail_page_commit(struct inode *inode)
 		folio_put(folio);
 		if (ret != -EBUSY)
 			return;
-		commit_tid = 0;
+		has_transaction = false;
 		read_lock(&journal->j_state_lock);
-		if (journal->j_committing_transaction)
+		if (journal->j_committing_transaction) {
 			commit_tid = journal->j_committing_transaction->t_tid;
+			has_transaction = true;
+		}
 		read_unlock(&journal->j_state_lock);
-		if (commit_tid)
+		if (has_transaction)
 			jbd2_log_wait_commit(journal, commit_tid);
 	}
 }