ext4: Retry block allocation if new blocks are allocated from system zone.

If the block allocator gets blocks out of system zone ext4 calls
ext4_error. But if the file system is mounted with errors=continue
retry block allocation. We need to mark the system zone blocks as
in use to make sure retry don't pick them again

System zone is the block range mapping block bitmap, inode bitmap and inode
table.

Signed-off-by: Aneesh Kumar K.V <[e-mail]>
Signed-off-by: Mingming Cao <[e-mail]>
Signed-off-by: "Theodore Ts'o" <[e-mail]>

fs/ext4/balloc.c

···
 			    (int)block_group, (unsigned long long)bitmap_blk);
 		return NULL;
 	}
-	if (!ext4_valid_block_bitmap(sb, desc, block_group, bh)) {
-		put_bh(bh);
-		return NULL;
-	}
-
+	ext4_valid_block_bitmap(sb, desc, block_group, bh);
+	/*
+	 * file system mounted not to panic on error,
+	 * continue with corrupt bitmap
+	 */
 	return bh;
 }
 /*
···
 			    "Allocating block in system zone - "
 			    "blocks from %llu, length %lu",
 			     ret_block, num);
-		goto out;
+		/*
+		 * claim_block marked the blocks we allocated
+		 * as in use. So we may want to selectively
+		 * mark some of the blocks as free
+		 */
+		goto retry_alloc;
 	}
 
 	performed_allocation = 1;

fs/ext4/mballoc.c

···
 	struct ext4_sb_info *sbi;
 	struct super_block *sb;
 	ext4_fsblk_t block;
-	int err;
+	int err, len;
 
 	BUG_ON(ac->ac_status != AC_STATUS_FOUND);
 	BUG_ON(ac->ac_b_ex.fe_len <= 0);
···
 		+ ac->ac_b_ex.fe_start
 		+ le32_to_cpu(es->s_first_data_block);
 
-	if (block == ext4_block_bitmap(sb, gdp) ||
-			block == ext4_inode_bitmap(sb, gdp) ||
-			in_range(block, ext4_inode_table(sb, gdp),
-				EXT4_SB(sb)->s_itb_per_group)) {
-
+	len = ac->ac_b_ex.fe_len;
+	if (in_range(ext4_block_bitmap(sb, gdp), block, len) ||
+	    in_range(ext4_inode_bitmap(sb, gdp), block, len) ||
+	    in_range(block, ext4_inode_table(sb, gdp),
+		     EXT4_SB(sb)->s_itb_per_group) ||
+	    in_range(block + len - 1, ext4_inode_table(sb, gdp),
+		     EXT4_SB(sb)->s_itb_per_group)) {
 		ext4_error(sb, __func__,
 			   "Allocating block in system zone - block = %llu",
 			   block);
+		/* File system mounted not to panic on error
+		 * Fix the bitmap and repeat the block allocation
+		 * We leak some of the blocks here.
+		 */
+		mb_set_bits(sb_bgl_lock(sbi, ac->ac_b_ex.fe_group),
+				bitmap_bh->b_data, ac->ac_b_ex.fe_start,
+				ac->ac_b_ex.fe_len);
+		err = ext4_journal_dirty_metadata(handle, bitmap_bh);
+		if (!err)
+			err = -EAGAIN;
+		goto out_err;
 	}
 #ifdef AGGRESSIVE_CHECK
 	{
···
 
 		ac->ac_op = EXT4_MB_HISTORY_ALLOC;
 		ext4_mb_normalize_request(ac, ar);
-
 repeat:
 		/* allocate space in core */
 		ext4_mb_regular_allocator(ac);
···
 	}
 
 	if (likely(ac->ac_status == AC_STATUS_FOUND)) {
-		ext4_mb_mark_diskspace_used(ac, handle);
-		*errp = 0;
-		block = ext4_grp_offs_to_block(sb, &ac->ac_b_ex);
-		ar->len = ac->ac_b_ex.fe_len;
+		*errp = ext4_mb_mark_diskspace_used(ac, handle);
+		if (*errp ==  -EAGAIN) {
+			ac->ac_b_ex.fe_group = 0;
+			ac->ac_b_ex.fe_start = 0;
+			ac->ac_b_ex.fe_len = 0;
+			ac->ac_status = AC_STATUS_CONTINUE;
+			goto repeat;
+		} else if (*errp) {
+			ac->ac_b_ex.fe_len = 0;
+			ar->len = 0;
+			ext4_mb_show_ac(ac);
+		} else {
+			block = ext4_grp_offs_to_block(sb, &ac->ac_b_ex);
+			ar->len = ac->ac_b_ex.fe_len;
+		}
 	} else {
 		freed  = ext4_mb_discard_preallocations(sb, ac->ac_o_ex.fe_len);
 		if (freed)
···
 		ext4_error(sb, __func__,
 			   "Freeing blocks in system zone - "
 			   "Block = %lu, count = %lu", block, count);
+		/* err = 0. ext4_std_error should be a no op */
+		goto error_return;
 	}
 
 	BUFFER_TRACE(bitmap_bh, "getting write access");