f2fs: compress: don't redirty sparse cluster during {,de}compress

In f2fs_do_write_data_page, when the data block is NULL_ADDR, it skips
writepage considering that it has been already truncated.
This results in an infinite loop as the PAGECACHE_TAG_TOWRITE tag is not
cleared during the writeback process for a compressed file including
NULL_ADDR in compress_mode=user.

This is the reproduction process:

1. dd if=/dev/zero bs=4096 count=1024 seek=1024 of=testfile
2. f2fs_io compress testfile
3. dd if=/dev/zero bs=4096 count=1 conv=notrunc of=testfile
4. f2fs_io decompress testfile

To prevent the problem, let's check whether the cluster is fully
allocated before redirty its pages.

Fixes: 5fdb322f ("f2fs: add F2FS_IOC_DECOMPRESS_FILE and F2FS_IOC_COMPRESS_FILE")
Reviewed-by: Sungjong Seo <sj1557.seo@samsung.com>
Reviewed-by: Sunmin Jeong <s_min.jeong@samsung.com>
Tested-by: Jaewook Kim <jw5454.kim@samsung.com>
Signed-off-by: Yeongjin Gil <youngjin.gil@samsung.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/compress.c

@@ -945,7 +945,7 @@ static int __f2fs_get_cluster_blocks(struct inode *inode,
 	unsigned int cluster_size = F2FS_I(inode)->i_cluster_size;
 	int count, i;
 
-	for (i = 1, count = 1; i < cluster_size; i++) {
+	for (i = 0, count = 0; i < cluster_size; i++) {
 		block_t blkaddr = data_blkaddr(dn->inode, dn->node_page,
 							dn->ofs_in_node + i);
 
@@ -956,8 +956,8 @@ static int __f2fs_get_cluster_blocks(struct inode *inode,
 	return count;
 }
 
-static int __f2fs_cluster_blocks(struct inode *inode,
-				unsigned int cluster_idx, bool compr_blks)
+static int __f2fs_cluster_blocks(struct inode *inode, unsigned int cluster_idx,
+				enum cluster_check_type type)
 {
 	struct dnode_of_data dn;
 	unsigned int start_idx = cluster_idx <<
@@ -978,10 +978,12 @@ static int __f2fs_cluster_blocks(struct inode *inode,
 	}
 
 	if (dn.data_blkaddr == COMPRESS_ADDR) {
-		if (compr_blks)
-			ret = __f2fs_get_cluster_blocks(inode, &dn);
-		else
+		if (type == CLUSTER_COMPR_BLKS)
+			ret = 1 + __f2fs_get_cluster_blocks(inode, &dn);
+		else if (type == CLUSTER_IS_COMPR)
 			ret = 1;
+	} else if (type == CLUSTER_RAW_BLKS) {
+		ret = __f2fs_get_cluster_blocks(inode, &dn);
 	}
 fail:
 	f2fs_put_dnode(&dn);
@@ -991,7 +993,16 @@ static int __f2fs_cluster_blocks(struct inode *inode,
 /* return # of compressed blocks in compressed cluster */
 static int f2fs_compressed_blocks(struct compress_ctx *cc)
 {
-	return __f2fs_cluster_blocks(cc->inode, cc->cluster_idx, true);
+	return __f2fs_cluster_blocks(cc->inode, cc->cluster_idx,
+		CLUSTER_COMPR_BLKS);
+}
+
+/* return # of raw blocks in non-compressed cluster */
+static int f2fs_decompressed_blocks(struct inode *inode,
+				unsigned int cluster_idx)
+{
+	return __f2fs_cluster_blocks(inode, cluster_idx,
+		CLUSTER_RAW_BLKS);
 }
 
 /* return whether cluster is compressed one or not */
@@ -999,7 +1010,16 @@ int f2fs_is_compressed_cluster(struct inode *inode, pgoff_t index)
 {
 	return __f2fs_cluster_blocks(inode,
 		index >> F2FS_I(inode)->i_log_cluster_size,
-		false);
+		CLUSTER_IS_COMPR);
+}
+
+/* return whether cluster contains non raw blocks or not */
+bool f2fs_is_sparse_cluster(struct inode *inode, pgoff_t index)
+{
+	unsigned int cluster_idx = index >> F2FS_I(inode)->i_log_cluster_size;
+
+	return f2fs_decompressed_blocks(inode, cluster_idx) !=
+		F2FS_I(inode)->i_cluster_size;
 }
 
 static bool cluster_may_compress(struct compress_ctx *cc)

fs/f2fs/f2fs.h

@@ -4302,6 +4302,11 @@ static inline bool f2fs_meta_inode_gc_required(struct inode *inode)
  * compress.c
  */
 #ifdef CONFIG_F2FS_FS_COMPRESSION
+enum cluster_check_type {
+	CLUSTER_IS_COMPR,   /* check only if compressed cluster */
+	CLUSTER_COMPR_BLKS, /* return # of compressed blocks in a cluster */
+	CLUSTER_RAW_BLKS    /* return # of raw blocks in a cluster */
+};
 bool f2fs_is_compressed_page(struct page *page);
 struct page *f2fs_compress_control_page(struct page *page);
 int f2fs_prepare_compress_overwrite(struct inode *inode,
@@ -4328,6 +4333,7 @@ int f2fs_write_multi_pages(struct compress_ctx *cc,
 						struct writeback_control *wbc,
 						enum iostat_type io_type);
 int f2fs_is_compressed_cluster(struct inode *inode, pgoff_t index);
+bool f2fs_is_sparse_cluster(struct inode *inode, pgoff_t index);
 void f2fs_update_read_extent_tree_range_compressed(struct inode *inode,
 				pgoff_t fofs, block_t blkaddr,
 				unsigned int llen, unsigned int c_len);
@@ -4414,6 +4420,12 @@ static inline bool f2fs_load_compressed_page(struct f2fs_sb_info *sbi,
 static inline void f2fs_invalidate_compress_pages(struct f2fs_sb_info *sbi,
 							nid_t ino) { }
 #define inc_compr_inode_stat(inode)		do { } while (0)
+static inline int f2fs_is_compressed_cluster(
+				struct inode *inode,
+				pgoff_t index) { return 0; }
+static inline bool f2fs_is_sparse_cluster(
+				struct inode *inode,
+				pgoff_t index) { return true; }
 static inline void f2fs_update_read_extent_tree_range_compressed(
 				struct inode *inode,
 				pgoff_t fofs, block_t blkaddr,

fs/f2fs/file.c

@@ -4236,9 +4236,8 @@ static int f2fs_ioc_decompress_file(struct file *filp)
 	struct inode *inode = file_inode(filp);
 	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
 	struct f2fs_inode_info *fi = F2FS_I(inode);
-	pgoff_t page_idx = 0, last_idx;
-	int cluster_size = fi->i_cluster_size;
-	int count, ret;
+	pgoff_t page_idx = 0, last_idx, cluster_idx;
+	int ret;
 
 	if (!f2fs_sb_has_compression(sbi) ||
 			F2FS_OPTION(sbi).compress_mode != COMPR_MODE_USER)
@@ -4273,10 +4272,15 @@ static int f2fs_ioc_decompress_file(struct file *filp)
 		goto out;
 
 	last_idx = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
+	last_idx >>= fi->i_log_cluster_size;
+
+	for (cluster_idx = 0; cluster_idx < last_idx; cluster_idx++) {
+		page_idx = cluster_idx << fi->i_log_cluster_size;
+
+		if (!f2fs_is_compressed_cluster(inode, page_idx))
+			continue;
 
-	count = last_idx - page_idx;
-	while (count && count >= cluster_size) {
-		ret = redirty_blocks(inode, page_idx, cluster_size);
+		ret = redirty_blocks(inode, page_idx, fi->i_cluster_size);
 		if (ret < 0)
 			break;
 
@@ -4286,9 +4290,6 @@ static int f2fs_ioc_decompress_file(struct file *filp)
 				break;
 		}
 
-		count -= cluster_size;
-		page_idx += cluster_size;
-
 		cond_resched();
 		if (fatal_signal_pending(current)) {
 			ret = -EINTR;
@@ -4315,9 +4316,9 @@ static int f2fs_ioc_compress_file(struct file *filp)
 {
 	struct inode *inode = file_inode(filp);
 	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
-	pgoff_t page_idx = 0, last_idx;
-	int cluster_size = F2FS_I(inode)->i_cluster_size;
-	int count, ret;
+	struct f2fs_inode_info *fi = F2FS_I(inode);
+	pgoff_t page_idx = 0, last_idx, cluster_idx;
+	int ret;
 
 	if (!f2fs_sb_has_compression(sbi) ||
 			F2FS_OPTION(sbi).compress_mode != COMPR_MODE_USER)
@@ -4351,10 +4352,15 @@ static int f2fs_ioc_compress_file(struct file *filp)
 	set_inode_flag(inode, FI_ENABLE_COMPRESS);
 
 	last_idx = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
+	last_idx >>= fi->i_log_cluster_size;
 
-	count = last_idx - page_idx;
-	while (count && count >= cluster_size) {
-		ret = redirty_blocks(inode, page_idx, cluster_size);
+	for (cluster_idx = 0; cluster_idx < last_idx; cluster_idx++) {
+		page_idx = cluster_idx << fi->i_log_cluster_size;
+
+		if (f2fs_is_sparse_cluster(inode, page_idx))
+			continue;
+
+		ret = redirty_blocks(inode, page_idx, fi->i_cluster_size);
 		if (ret < 0)
 			break;
 
@@ -4364,9 +4370,6 @@ static int f2fs_ioc_compress_file(struct file *filp)
 				break;
 		}
 
-		count -= cluster_size;
-		page_idx += cluster_size;
-
 		cond_resched();
 		if (fatal_signal_pending(current)) {
 			ret = -EINTR;