[PATCH v3 3/4] f2fs: Fix accounting for unusable blocks

[Daniel Rosenberg]

Fixes possible underflows when dealing with unusable blocks.

Signed-off-by: Daniel Rosenberg <dro...@google.com>
---
 fs/f2fs/f2fs.h | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 9b3d9977cd1ef..a39cc4ffeb4b1 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1769,8 +1769,12 @@ static inline int inc_valid_block_count(struct 
f2fs_sb_info *sbi,
 
        if (!__allow_reserved_blocks(sbi, inode, true))
                avail_user_block_count -= F2FS_OPTION(sbi).root_reserved_blocks;
-       if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED)))
-               avail_user_block_count -= sbi->unusable_block_count;
+       if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED))) {
+               if (avail_user_block_count > sbi->unusable_block_count)
+                       avail_user_block_count = 0;
+               else
+                       avail_user_block_count -= sbi->unusable_block_count;
+       }
        if (unlikely(sbi->total_valid_block_count > avail_user_block_count)) {
                diff = sbi->total_valid_block_count - avail_user_block_count;
                if (diff > *count)
@@ -1970,7 +1974,7 @@ static inline int inc_valid_node_count(struct 
f2fs_sb_info *sbi,
                                        struct inode *inode, bool is_inode)
 {
        block_t valid_block_count;
-       unsigned int valid_node_count;
+       unsigned int valid_node_count, user_block_count;
        int err;
 
        if (is_inode) {
@@ -1997,10 +2001,11 @@ static inline int inc_valid_node_count(struct 
f2fs_sb_info *sbi,
 
        if (!__allow_reserved_blocks(sbi, inode, false))
                valid_block_count += F2FS_OPTION(sbi).root_reserved_blocks;
+       user_block_count = sbi->user_block_count;
        if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED)))
-               valid_block_count += sbi->unusable_block_count;
+               user_block_count -= sbi->unusable_block_count;
 
-       if (unlikely(valid_block_count > sbi->user_block_count)) {
+       if (unlikely(valid_block_count > user_block_count)) {
                spin_unlock(&sbi->stat_lock);
                goto enospc;
        }
-- 
2.22.0.rc1.257.g3120a18244-goog