f2fs: rework write preallocations

f2fs_write_begin() assumes that all blocks were preallocated by
default unless FI_NO_PREALLOC is explicitly set.  This invites data
corruption, as there are cases in which not all blocks are preallocated.
Commit 47501f87 ("f2fs: preallocate DIO blocks when forcing
buffered_io") fixed one case, but there are others remaining.

Fix up this logic by replacing this flag with FI_PREALLOCATED_ALL, which
only gets set if all blocks for the current write were preallocated.

Also clean up f2fs_preallocate_blocks(), move it to file.c, and make it
handle some of the logic that was previously in write_iter() directly.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -1384,53 +1384,6 @@ static int __allocate_data_block(struct dnode_of_data *dn, int seg_type)
 	return 0;
 }
 
-int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from)
-{
-	struct inode *inode = file_inode(iocb->ki_filp);
-	struct f2fs_map_blocks map;
-	int flag;
-	int err = 0;
-	bool direct_io = iocb->ki_flags & IOCB_DIRECT;
-
-	map.m_lblk = F2FS_BLK_ALIGN(iocb->ki_pos);
-	map.m_len = F2FS_BYTES_TO_BLK(iocb->ki_pos + iov_iter_count(from));
-	if (map.m_len > map.m_lblk)
-		map.m_len -= map.m_lblk;
-	else
-		map.m_len = 0;
-
-	map.m_next_pgofs = NULL;
-	map.m_next_extent = NULL;
-	map.m_seg_type = NO_CHECK_TYPE;
-	map.m_may_create = true;
-
-	if (direct_io) {
-		map.m_seg_type = f2fs_rw_hint_to_seg_type(iocb->ki_hint);
-		flag = f2fs_force_buffered_io(inode, iocb, from) ?
-					F2FS_GET_BLOCK_PRE_AIO :
-					F2FS_GET_BLOCK_PRE_DIO;
-		goto map_blocks;
-	}
-	if (iocb->ki_pos + iov_iter_count(from) > MAX_INLINE_DATA(inode)) {
-		err = f2fs_convert_inline_inode(inode);
-		if (err)
-			return err;
-	}
-	if (f2fs_has_inline_data(inode))
-		return err;
-
-	flag = F2FS_GET_BLOCK_PRE_AIO;
-
-map_blocks:
-	err = f2fs_map_blocks(inode, &map, 1, flag);
-	if (map.m_len > 0 && err == -ENOSPC) {
-		if (!direct_io)
-			set_inode_flag(inode, FI_NO_PREALLOC);
-		err = 0;
-	}
-	return err;
-}
-
 void f2fs_do_map_lock(struct f2fs_sb_info *sbi, int flag, bool lock)
 {
 	if (flag == F2FS_GET_BLOCK_PRE_AIO) {
@@ -3340,12 +3293,10 @@ static int prepare_write_begin(struct f2fs_sb_info *sbi,
 	int flag;
 
 	/*
-	 * we already allocated all the blocks, so we don't need to get
-	 * the block addresses when there is no need to fill the page.
+	 * If a whole page is being written and we already preallocated all the
+	 * blocks, then there is no need to get a block address now.
 	 */
-	if (!f2fs_has_inline_data(inode) && len == PAGE_SIZE &&
-	    !is_inode_flag_set(inode, FI_NO_PREALLOC) &&
-	    !f2fs_verity_in_progress(inode))
+	if (len == PAGE_SIZE && is_inode_flag_set(inode, FI_PREALLOCATED_ALL))
 		return 0;
 
 	/* f2fs_lock_op avoids race between write CP and convert_inline_page */

fs/f2fs/f2fs.h

@@ -715,7 +715,7 @@ enum {
 	FI_INLINE_DOTS,		/* indicate inline dot dentries */
 	FI_DO_DEFRAG,		/* indicate defragment is running */
 	FI_DIRTY_FILE,		/* indicate regular/symlink has dirty pages */
-	FI_NO_PREALLOC,		/* indicate skipped preallocated blocks */
+	FI_PREALLOCATED_ALL,	/* all blocks for write were preallocated */
 	FI_HOT_DATA,		/* indicate file is hot */
 	FI_EXTRA_ATTR,		/* indicate file has extra attribute */
 	FI_PROJ_INHERIT,	/* indicate file inherits projectid */
@@ -3615,7 +3615,6 @@ void f2fs_update_data_blkaddr(struct dnode_of_data *dn, block_t blkaddr);
 int f2fs_reserve_new_blocks(struct dnode_of_data *dn, blkcnt_t count);
 int f2fs_reserve_new_block(struct dnode_of_data *dn);
 int f2fs_get_block(struct dnode_of_data *dn, pgoff_t index);
-int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from);
 int f2fs_reserve_block(struct dnode_of_data *dn, pgoff_t index);
 struct page *f2fs_get_read_data_page(struct inode *inode, pgoff_t index,
 			int op_flags, bool for_write);

fs/f2fs/file.c

@@ -4235,10 +4235,77 @@ static ssize_t f2fs_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
 	return ret;
 }
 
+/*
+ * Preallocate blocks for a write request, if it is possible and helpful to do
+ * so.  Returns a positive number if blocks may have been preallocated, 0 if no
+ * blocks were preallocated, or a negative errno value if something went
+ * seriously wrong.  Also sets FI_PREALLOCATED_ALL on the inode if *all* the
+ * requested blocks (not just some of them) have been allocated.
+ */
+static int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *iter)
+{
+	struct inode *inode = file_inode(iocb->ki_filp);
+	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
+	const loff_t pos = iocb->ki_pos;
+	const size_t count = iov_iter_count(iter);
+	struct f2fs_map_blocks map = {};
+	bool dio = (iocb->ki_flags & IOCB_DIRECT) &&
+		   !f2fs_force_buffered_io(inode, iocb, iter);
+	int flag;
+	int ret;
+
+	/* If it will be an out-of-place direct write, don't bother. */
+	if (dio && f2fs_lfs_mode(sbi))
+		return 0;
+
+	/* No-wait I/O can't allocate blocks. */
+	if (iocb->ki_flags & IOCB_NOWAIT)
+		return 0;
+
+	/* If it will be a short write, don't bother. */
+	if (fault_in_iov_iter_readable(iter, count))
+		return 0;
+
+	if (f2fs_has_inline_data(inode)) {
+		/* If the data will fit inline, don't bother. */
+		if (pos + count <= MAX_INLINE_DATA(inode))
+			return 0;
+		ret = f2fs_convert_inline_inode(inode);
+		if (ret)
+			return ret;
+	}
+
+	/* Do not preallocate blocks that will be written partially in 4KB. */
+	map.m_lblk = F2FS_BLK_ALIGN(pos);
+	map.m_len = F2FS_BYTES_TO_BLK(pos + count);
+	if (map.m_len > map.m_lblk)
+		map.m_len -= map.m_lblk;
+	else
+		map.m_len = 0;
+	map.m_may_create = true;
+	if (dio) {
+		map.m_seg_type = f2fs_rw_hint_to_seg_type(inode->i_write_hint);
+		flag = F2FS_GET_BLOCK_PRE_DIO;
+	} else {
+		map.m_seg_type = NO_CHECK_TYPE;
+		flag = F2FS_GET_BLOCK_PRE_AIO;
+	}
+
+	ret = f2fs_map_blocks(inode, &map, 1, flag);
+	/* -ENOSPC is only a fatal error if no blocks could be allocated. */
+	if (ret < 0 && !(ret == -ENOSPC && map.m_len > 0))
+		return ret;
+	if (ret == 0)
+		set_inode_flag(inode, FI_PREALLOCATED_ALL);
+	return map.m_len;
+}
+
 static ssize_t f2fs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 {
 	struct file *file = iocb->ki_filp;
 	struct inode *inode = file_inode(file);
+	loff_t target_size;
+	int preallocated;
 	ssize_t ret;
 
 	if (unlikely(f2fs_cp_error(F2FS_I_SB(inode)))) {
@@ -4262,84 +4329,54 @@ static ssize_t f2fs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 
 	if (unlikely(IS_IMMUTABLE(inode))) {
 		ret = -EPERM;
-		goto unlock;
+		goto out_unlock;
 	}
 
 	if (is_inode_flag_set(inode, FI_COMPRESS_RELEASED)) {
 		ret = -EPERM;
-		goto unlock;
+		goto out_unlock;
 	}
 
 	ret = generic_write_checks(iocb, from);
 	if (ret > 0) {
-		bool preallocated = false;
-		size_t target_size = 0;
-		int err;
-
-		if (fault_in_iov_iter_readable(from, iov_iter_count(from)))
-			set_inode_flag(inode, FI_NO_PREALLOC);
-
-		if ((iocb->ki_flags & IOCB_NOWAIT)) {
+		if (iocb->ki_flags & IOCB_NOWAIT) {
 			if (!f2fs_overwrite_io(inode, iocb->ki_pos,
 						iov_iter_count(from)) ||
 				f2fs_has_inline_data(inode) ||
 				f2fs_force_buffered_io(inode, iocb, from)) {
-				clear_inode_flag(inode, FI_NO_PREALLOC);
-				inode_unlock(inode);
 				ret = -EAGAIN;
-				goto out;
+				goto out_unlock;
 			}
-			goto write;
 		}
-
-		if (is_inode_flag_set(inode, FI_NO_PREALLOC))
-			goto write;
-
 		if (iocb->ki_flags & IOCB_DIRECT) {
-			/*
-			 * Convert inline data for Direct I/O before entering
-			 * f2fs_direct_IO().
-			 */
-			err = f2fs_convert_inline_inode(inode);
-			if (err)
-				goto out_err;
-			/*
-			 * If force_buffere_io() is true, we have to allocate
-			 * blocks all the time, since f2fs_direct_IO will fall
-			 * back to buffered IO.
-			 */
-			if (!f2fs_force_buffered_io(inode, iocb, from) &&
-					f2fs_lfs_mode(F2FS_I_SB(inode)))
-				goto write;
+			ret = f2fs_convert_inline_inode(inode);
+			if (ret)
+				goto out_unlock;
 		}
-		preallocated = true;
+		/* Possibly preallocate the blocks for the write. */
 		target_size = iocb->ki_pos + iov_iter_count(from);
-
-		err = f2fs_preallocate_blocks(iocb, from);
-		if (err) {
-out_err:
-			clear_inode_flag(inode, FI_NO_PREALLOC);
-			inode_unlock(inode);
-			ret = err;
-			goto out;
+		preallocated = f2fs_preallocate_blocks(iocb, from);
+		if (preallocated < 0) {
+			ret = preallocated;
+			goto out_unlock;
 		}
-write:
+
 		ret = __generic_file_write_iter(iocb, from);
-		clear_inode_flag(inode, FI_NO_PREALLOC);
 
-		/* if we couldn't write data, we should deallocate blocks. */
-		if (preallocated && i_size_read(inode) < target_size) {
+		/* Don't leave any preallocated blocks around past i_size. */
+		if (preallocated > 0 && i_size_read(inode) < target_size) {
 			down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
 			filemap_invalidate_lock(inode->i_mapping);
 			f2fs_truncate(inode);
 			filemap_invalidate_unlock(inode->i_mapping);
 			up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
 		}
+		clear_inode_flag(inode, FI_PREALLOCATED_ALL);
 
 		if (ret > 0)
 			f2fs_update_iostat(F2FS_I_SB(inode), APP_WRITE_IO, ret);
 	}
-unlock:
+out_unlock:
 	inode_unlock(inode);
 out:
 	trace_f2fs_file_write_iter(inode, iocb->ki_pos,