ext4: always allocate blocks only from groups inode can use

For filesystems with more than 2^32 blocks inodes using indirect block
based format cannot use blocks beyond the 32-bit limit.
ext4_mb_scan_groups_linear() takes care to not select these unsupported
groups for such inodes however other functions selecting groups for
allocation don't. So far this is harmless because the other selection
functions are used only with mb_optimize_scan and this is currently
disabled for inodes with indirect blocks however in the following patch
we want to enable mb_optimize_scan regardless of inode format.

Reviewed-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Acked-by: Pedro Falcato <pfalcato@suse.de>
Cc: stable@kernel.org
Link: https://patch.msgid.link/20260114182836.14120-3-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Author: jankara

fs/ext4/mballoc.c

@@ -892,14 +892,29 @@ mb_update_avg_fragment_size(struct super_block *sb, struct ext4_group_info *grp)
 	}
 }
 
+static ext4_group_t ext4_get_allocation_groups_count(
+				struct ext4_allocation_context *ac)
+{
+	ext4_group_t ngroups = ext4_get_groups_count(ac->ac_sb);
+
+	/* non-extent files are limited to low blocks/groups */
+	if (!(ext4_test_inode_flag(ac->ac_inode, EXT4_INODE_EXTENTS)))
+		ngroups = EXT4_SB(ac->ac_sb)->s_blockfile_groups;
+
+	/* Pairs with smp_wmb() in ext4_update_super() */
+	smp_rmb();
+
+	return ngroups;
+}
+
 static int ext4_mb_scan_groups_xa_range(struct ext4_allocation_context *ac,
 					struct xarray *xa,
 					ext4_group_t start, ext4_group_t end)
 {
 	struct super_block *sb = ac->ac_sb;
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
 	enum criteria cr = ac->ac_criteria;
-	ext4_group_t ngroups = ext4_get_groups_count(sb);
+	ext4_group_t ngroups = ext4_get_allocation_groups_count(ac);
 	unsigned long group = start;
 	struct ext4_group_info *grp;
 
@@ -951,7 +966,7 @@ static int ext4_mb_scan_groups_p2_aligned(struct ext4_allocation_context *ac,
 	ext4_group_t start, end;
 
 	start = group;
-	end = ext4_get_groups_count(ac->ac_sb);
+	end = ext4_get_allocation_groups_count(ac);
 wrap_around:
 	for (i = ac->ac_2order; i < MB_NUM_ORDERS(ac->ac_sb); i++) {
 		ret = ext4_mb_scan_groups_largest_free_order_range(ac, i,
@@ -1001,7 +1016,7 @@ static int ext4_mb_scan_groups_goal_fast(struct ext4_allocation_context *ac,
 	ext4_group_t start, end;
 
 	start = group;
-	end = ext4_get_groups_count(ac->ac_sb);
+	end = ext4_get_allocation_groups_count(ac);
 wrap_around:
 	i = mb_avg_fragment_size_order(ac->ac_sb, ac->ac_g_ex.fe_len);
 	for (; i < MB_NUM_ORDERS(ac->ac_sb); i++) {
@@ -1083,7 +1098,7 @@ static int ext4_mb_scan_groups_best_avail(struct ext4_allocation_context *ac,
 		min_order = fls(ac->ac_o_ex.fe_len);
 
 	start = group;
-	end = ext4_get_groups_count(ac->ac_sb);
+	end = ext4_get_allocation_groups_count(ac);
 wrap_around:
 	for (i = order; i >= min_order; i--) {
 		int frag_order;
@@ -1182,11 +1197,7 @@ static int ext4_mb_scan_groups(struct ext4_allocation_context *ac)
 	int ret = 0;
 	ext4_group_t start;
 	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
-	ext4_group_t ngroups = ext4_get_groups_count(ac->ac_sb);
-
-	/* non-extent files are limited to low blocks/groups */
-	if (!(ext4_test_inode_flag(ac->ac_inode, EXT4_INODE_EXTENTS)))
-		ngroups = sbi->s_blockfile_groups;
+	ext4_group_t ngroups = ext4_get_allocation_groups_count(ac);
 
 	/* searching for the right group start from the goal value specified */
 	start = ac->ac_g_ex.fe_group;