jbd2: do not try to recover wiped journal

If a journal is wiped, we will set journal->j_tail to 0. However if
'write' argument is not set (as it happens for read-only device or for
ocfs2), the on-disk superblock is not updated accordingly and thus
jbd2_journal_recover() cat try to recover the wiped journal. Fix the
check in jbd2_journal_recover() to use journal->j_tail for checking
empty journal instead.

Signed-off-by: Jan Kara <[email protected]>
Reviewed-by: Zhang Yi <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Theodore Ts'o <[email protected]>

Author: jankara

fs/jbd2/recovery.c

@@ -282,19 +282,20 @@ static int fc_do_one_pass(journal_t *journal,
 int jbd2_journal_recover(journal_t *journal)
 {
 	int			err, err2;
-	journal_superblock_t *	sb;
-
 	struct recovery_info	info;
 
 	memset(&info, 0, sizeof(info));
-	sb = journal->j_superblock;
 
 	/*
 	 * The journal superblock's s_start field (the current log head)
 	 * is always zero if, and only if, the journal was cleanly
-	 * unmounted.
+	 * unmounted. We use its in-memory version j_tail here because
+	 * jbd2_journal_wipe() could have updated it without updating journal
+	 * superblock.
 	 */
-	if (!sb->s_start) {
+	if (!journal->j_tail) {
+		journal_superblock_t *sb = journal->j_superblock;
+
 		jbd2_debug(1, "No recovery required, last transaction %d, head block %u\n",
 			  be32_to_cpu(sb->s_sequence), be32_to_cpu(sb->s_head));
 		journal->j_transaction_sequence = be32_to_cpu(sb->s_sequence) + 1;