[PATCH] f2fs: fix valid block count leak on data block allocation failure

[Chen Changcheng <chenchangcheng@kylinos.cn>]

In __allocate_data_block(), when allocating a new data block
(dn->data_blkaddr == NULL_ADDR), inc_valid_block_count() is
called first to increment total_valid_block_count and i_blocks.
If the subsequent f2fs_allocate_data_block() fails, the function
returns the error directly without rolling back the
already-incremented block counts, causing a permanent leak.

Fix this by calling dec_valid_block_count() to undo the
increment before returning the error. The condition
old_blkaddr == NULL_ADDR precisely identifies the case where
inc_valid_block_count() was called.

Signed-off-by: Chen Changcheng <chenchangcheng@kylinos.cn>
---
 fs/f2fs/data.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index a765fda71536..819631bb61ae 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -1532,8 +1532,11 @@ static int __allocate_data_block(struct dnode_of_data *dn, int seg_type)
 	old_blkaddr = dn->data_blkaddr;
 	err = f2fs_allocate_data_block(sbi, NULL, old_blkaddr,
 				&dn->data_blkaddr, &sum, seg_type, NULL);
-	if (err)
+	if (err) {
+		if (old_blkaddr == NULL_ADDR)
+			dec_valid_block_count(sbi, dn->inode, count);
 		return err;
+	}
 
 	if (GET_SEGNO(sbi, old_blkaddr) != NULL_SEGNO)
 		f2fs_invalidate_internal_cache(sbi, old_blkaddr, 1);
-- 
2.25.1