ext4: factor out codes to update block bitmap and group descriptor on disk from ext4_mb_mark_bb

There are several reasons to add a general function ext4_mb_mark_context
to update block bitmap and group descriptor on disk:
1. pair behavior of alloc/free bits. For example,
ext4_mb_new_blocks_simple will update free_clusters in struct flex_groups
in ext4_mb_mark_bb while ext4_free_blocks_simple forgets this.
2. remove repeat code to read from disk, update and write back to disk.
3. reduce future unit test mocks to catch real IO to update structure
on disk.

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: "Ritesh Harjani (IBM)" <ritesh.list@gmail.com>
Link: https://lore.kernel.org/r/20230928160407.142069-3-shikemeng@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Author: Kemeng Shi

fs/ext4/mballoc.c

@@ -3943,6 +3943,80 @@ void ext4_exit_mballoc(void)
 	ext4_groupinfo_destroy_slabs();
 }
 
+static int
+ext4_mb_mark_context(struct super_block *sb, bool state, ext4_group_t group,
+		     ext4_grpblk_t blkoff, ext4_grpblk_t len)
+{
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	struct buffer_head *bitmap_bh = NULL;
+	struct ext4_group_desc *gdp;
+	struct buffer_head *gdp_bh;
+	int err;
+	unsigned int i, already, changed;
+
+	bitmap_bh = ext4_read_block_bitmap(sb, group);
+	if (IS_ERR(bitmap_bh))
+		return PTR_ERR(bitmap_bh);
+
+	err = -EIO;
+	gdp = ext4_get_group_desc(sb, group, &gdp_bh);
+	if (!gdp)
+		goto out_err;
+
+	ext4_lock_group(sb, group);
+	if (ext4_has_group_desc_csum(sb) &&
+	    (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT))) {
+		gdp->bg_flags &= cpu_to_le16(~EXT4_BG_BLOCK_UNINIT);
+		ext4_free_group_clusters_set(sb, gdp,
+			ext4_free_clusters_after_init(sb, group, gdp));
+	}
+
+	already = 0;
+	for (i = 0; i < len; i++)
+		if (mb_test_bit(blkoff + i, bitmap_bh->b_data) ==
+				state)
+			already++;
+	changed = len - already;
+
+	if (state) {
+		mb_set_bits(bitmap_bh->b_data, blkoff, len);
+		ext4_free_group_clusters_set(sb, gdp,
+			ext4_free_group_clusters(sb, gdp) - changed);
+	} else {
+		mb_clear_bits(bitmap_bh->b_data, blkoff, len);
+		ext4_free_group_clusters_set(sb, gdp,
+			ext4_free_group_clusters(sb, gdp) + changed);
+	}
+
+	ext4_block_bitmap_csum_set(sb, gdp, bitmap_bh);
+	ext4_group_desc_csum_set(sb, group, gdp);
+	ext4_unlock_group(sb, group);
+
+	if (sbi->s_log_groups_per_flex) {
+		ext4_group_t flex_group = ext4_flex_group(sbi, group);
+		struct flex_groups *fg = sbi_array_rcu_deref(sbi,
+					   s_flex_groups, flex_group);
+
+		if (state)
+			atomic64_sub(changed, &fg->free_clusters);
+		else
+			atomic64_add(changed, &fg->free_clusters);
+	}
+
+	err = ext4_handle_dirty_metadata(NULL, NULL, bitmap_bh);
+	if (err)
+		goto out_err;
+	err = ext4_handle_dirty_metadata(NULL, NULL, gdp_bh);
+	if (err)
+		goto out_err;
+
+	sync_dirty_buffer(bitmap_bh);
+	sync_dirty_buffer(gdp_bh);
+
+out_err:
+	brelse(bitmap_bh);
+	return err;
+}
 
 /*
  * Check quota and mark chosen space (ac->ac_b_ex) non-free in bitmaps
@@ -4069,15 +4143,11 @@ ext4_mb_mark_diskspace_used(struct ext4_allocation_context *ac,
 void ext4_mb_mark_bb(struct super_block *sb, ext4_fsblk_t block,
 		     int len, bool state)
 {
-	struct buffer_head *bitmap_bh = NULL;
-	struct ext4_group_desc *gdp;
-	struct buffer_head *gdp_bh;
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
 	ext4_group_t group;
 	ext4_grpblk_t blkoff;
-	int i, err = 0;
-	int already;
-	unsigned int clen, clen_changed, thisgrp_len;
+	int err = 0;
+	unsigned int clen, thisgrp_len;
 
 	while (len > 0) {
 		ext4_get_group_no_and_offset(sb, block, &group, &blkoff);
@@ -4098,80 +4168,17 @@ void ext4_mb_mark_bb(struct super_block *sb, ext4_fsblk_t block,
 			ext4_error(sb, "Marking blocks in system zone - "
 				   "Block = %llu, len = %u",
 				   block, thisgrp_len);
-			bitmap_bh = NULL;
 			break;
 		}
 
-		bitmap_bh = ext4_read_block_bitmap(sb, group);
-		if (IS_ERR(bitmap_bh)) {
-			err = PTR_ERR(bitmap_bh);
-			bitmap_bh = NULL;
-			break;
-		}
-
-		err = -EIO;
-		gdp = ext4_get_group_desc(sb, group, &gdp_bh);
-		if (!gdp)
-			break;
-
-		ext4_lock_group(sb, group);
-		already = 0;
-		for (i = 0; i < clen; i++)
-			if (!mb_test_bit(blkoff + i, bitmap_bh->b_data) ==
-					 !state)
-				already++;
-
-		clen_changed = clen - already;
-		if (state)
-			mb_set_bits(bitmap_bh->b_data, blkoff, clen);
-		else
-			mb_clear_bits(bitmap_bh->b_data, blkoff, clen);
-		if (ext4_has_group_desc_csum(sb) &&
-		    (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT))) {
-			gdp->bg_flags &= cpu_to_le16(~EXT4_BG_BLOCK_UNINIT);
-			ext4_free_group_clusters_set(sb, gdp,
-			     ext4_free_clusters_after_init(sb, group, gdp));
-		}
-		if (state)
-			clen = ext4_free_group_clusters(sb, gdp) - clen_changed;
-		else
-			clen = ext4_free_group_clusters(sb, gdp) + clen_changed;
-
-		ext4_free_group_clusters_set(sb, gdp, clen);
-		ext4_block_bitmap_csum_set(sb, gdp, bitmap_bh);
-		ext4_group_desc_csum_set(sb, group, gdp);
-
-		ext4_unlock_group(sb, group);
-
-		if (sbi->s_log_groups_per_flex) {
-			ext4_group_t flex_group = ext4_flex_group(sbi, group);
-			struct flex_groups *fg = sbi_array_rcu_deref(sbi,
-						   s_flex_groups, flex_group);
-
-			if (state)
-				atomic64_sub(clen_changed, &fg->free_clusters);
-			else
-				atomic64_add(clen_changed, &fg->free_clusters);
-
-		}
-
-		err = ext4_handle_dirty_metadata(NULL, NULL, bitmap_bh);
-		if (err)
-			break;
-		sync_dirty_buffer(bitmap_bh);
-		err = ext4_handle_dirty_metadata(NULL, NULL, gdp_bh);
-		sync_dirty_buffer(gdp_bh);
+		err = ext4_mb_mark_context(sb, state, group, blkoff, clen);
 		if (err)
 			break;
 
 		block += thisgrp_len;
 		len -= thisgrp_len;
-		brelse(bitmap_bh);
 		BUG_ON(len < 0);
 	}
-
-	if (err)
-		brelse(bitmap_bh);
 }
 
 /*