linux-ext4 - [RFC PATCH] jbd2: make '0' an invalid transaction sequence

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Message-ID: <87wmlrkkch.fsf_-_@linux.dev>
Date: Fri, 12 Jul 2024 10:53:02 +0100
From: Luis Henriques <luis.henriques@...ux.dev>
To: Andreas Dilger <adilger@...ger.ca>
Cc:  Wang Jianjian <wangjianjian0@...mail.com>,  "wangjianjian (C)"
 <wangjianjian3@...wei.com>,  Theodore Ts'o <tytso@....edu>,  Jan Kara
 <jack@...e.cz>,  Harshad Shirwadkar <harshadshirwadkar@...il.com>,
  linux-ext4@...r.kernel.org,  linux-kernel@...r.kernel.org
Subject: [RFC PATCH] jbd2: make '0' an invalid transaction sequence

Since there's code (in fast-commit) that already handles a '0' tid as a
special case, it's better to ensure that jbd2 never sets it to that value
when journal->j_transaction_sequence increment wraps.

Suggested-by: Andreas Dilger <adilger@...ger.ca>
Signed-off-by: Luis Henriques (SUSE) <luis.henriques@...ux.dev>
---
 fs/jbd2/transaction.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index 66513c18ca29..4dbdd37349c3 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -84,6 +84,8 @@ static void jbd2_get_transaction(journal_t *journal,
 	transaction->t_state = T_RUNNING;
 	transaction->t_start_time = ktime_get();
 	transaction->t_tid = journal->j_transaction_sequence++;
+	if (unlikely(transaction->t_tid == 0))
+		transaction->t_tid = journal->j_transaction_sequence++;
 	transaction->t_expires = jiffies + journal->j_commit_interval;
 	atomic_set(&transaction->t_updates, 0);
 	atomic_set(&transaction->t_outstanding_credits,