ext4: don't over-report free space or inodes in statvfs

JIRA: https://issues.redhat.com/browse/RHEL-89589

commit f87d3af
Author: Theodore Ts'o <tytso@mit.edu>
Date:   Fri Mar 14 00:38:42 2025 -0400

    ext4: don't over-report free space or inodes in statvfs

    This fixes an analogus bug that was fixed in xfs in commit
    4b8d867 ("xfs: don't over-report free space or inodes in
    statvfs") where statfs can report misleading / incorrect information
    where project quota is enabled, and the free space is less than the
    remaining quota.

    This commit will resolve a test failure in generic/762 which tests for
    this bug.

    Cc: stable@kernel.org
    Fixes: 689c958 ("ext4: add project quota support")
    Signed-off-by: Theodore Ts'o <tytso@mit.edu>
    Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

Signed-off-by: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>

Author: CKI Backport Bot

fs/ext4/super.c

@@ -6780,22 +6780,29 @@ static int ext4_statfs_project(struct super_block *sb,
 			     dquot->dq_dqb.dqb_bhardlimit);
 	limit >>= sb->s_blocksize_bits;
 
-	if (limit && buf->f_blocks > limit) {
+	if (limit) {
+		uint64_t	remaining = 0;
+
 		curblock = (dquot->dq_dqb.dqb_curspace +
 			    dquot->dq_dqb.dqb_rsvspace) >> sb->s_blocksize_bits;
-		buf->f_blocks = limit;
-		buf->f_bfree = buf->f_bavail =
-			(buf->f_blocks > curblock) ?
-			 (buf->f_blocks - curblock) : 0;
+		if (limit > curblock)
+			remaining = limit - curblock;
+
+		buf->f_blocks = min(buf->f_blocks, limit);
+		buf->f_bfree = min(buf->f_bfree, remaining);
+		buf->f_bavail = min(buf->f_bavail, remaining);
 	}
 
 	limit = min_not_zero(dquot->dq_dqb.dqb_isoftlimit,
 			     dquot->dq_dqb.dqb_ihardlimit);
-	if (limit && buf->f_files > limit) {
-		buf->f_files = limit;
-		buf->f_ffree =
-			(buf->f_files > dquot->dq_dqb.dqb_curinodes) ?
-			 (buf->f_files - dquot->dq_dqb.dqb_curinodes) : 0;
+	if (limit) {
+		uint64_t	remaining = 0;
+
+		if (limit > dquot->dq_dqb.dqb_curinodes)
+			remaining = limit - dquot->dq_dqb.dqb_curinodes;
+
+		buf->f_files = min(buf->f_files, limit);
+		buf->f_ffree = min(buf->f_ffree, remaining);
 	}
 
 	spin_unlock(&dquot->dq_dqb_lock);