ext4: fix possible tid_t sequence overflows

In the fast commit code there are a few places where tid_t variables are
being compared without taking into account the fact that these sequence
numbers may wrap.  Fix this issue by using the helper functions tid_gt()
and tid_geq().

Signed-off-by: Luis Henriques (SUSE) <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Reviewed-by: Harshad Shirwadkar <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Theodore Ts'o <[email protected]>

Author: Luis Henriques (SUSE)

fs/ext4/fast_commit.c

@@ -353,7 +353,7 @@ void ext4_fc_mark_ineligible(struct super_block *sb, int reason, handle_t *handl
 		read_unlock(&sbi->s_journal->j_state_lock);
 	}
 	spin_lock(&sbi->s_fc_lock);
-	if (sbi->s_fc_ineligible_tid < tid)
+	if (tid_gt(tid, sbi->s_fc_ineligible_tid))
 		sbi->s_fc_ineligible_tid = tid;
 	spin_unlock(&sbi->s_fc_lock);
 	WARN_ON(reason >= EXT4_FC_REASON_MAX);
@@ -1207,7 +1207,7 @@ int ext4_fc_commit(journal_t *journal, tid_t commit_tid)
 	if (ret == -EALREADY) {
 		/* There was an ongoing commit, check if we need to restart */
 		if (atomic_read(&sbi->s_fc_subtid) <= subtid &&
-			commit_tid > journal->j_commit_sequence)
+		    tid_gt(commit_tid, journal->j_commit_sequence))
 			goto restart_fc;
 		ext4_fc_update_stats(sb, EXT4_FC_STATUS_SKIPPED, 0, 0,
 				commit_tid);
@@ -1282,7 +1282,7 @@ static void ext4_fc_cleanup(journal_t *journal, int full, tid_t tid)
 		list_del_init(&iter->i_fc_list);
 		ext4_clear_inode_state(&iter->vfs_inode,
 				       EXT4_STATE_FC_COMMITTING);
-		if (iter->i_sync_tid <= tid)
+		if (tid_geq(tid, iter->i_sync_tid))
 			ext4_fc_reset_inode(&iter->vfs_inode);
 		/* Make sure EXT4_STATE_FC_COMMITTING bit is clear */
 		smp_mb();
@@ -1313,7 +1313,7 @@ static void ext4_fc_cleanup(journal_t *journal, int full, tid_t tid)
 	list_splice_init(&sbi->s_fc_q[FC_Q_STAGING],
 				&sbi->s_fc_q[FC_Q_MAIN]);
 
-	if (tid >= sbi->s_fc_ineligible_tid) {
+	if (tid_geq(tid, sbi->s_fc_ineligible_tid)) {
 		sbi->s_fc_ineligible_tid = 0;
 		ext4_clear_mount_flag(sb, EXT4_MF_FC_INELIGIBLE);
 	}