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Date:   Wed, 29 May 2019 17:49:05 -0700
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Subject: [PATCH v3 3/4] f2fs: Fix accounting for unusable blocks
From:   Daniel Rosenberg <drosen@google.com>
To:     Jaegeuk Kim <jaegeuk@kernel.org>, Chao Yu <yuchao0@huawei.com>,
        Jonathan Corbet <corbet@lwn.net>,
        linux-f2fs-devel@lists.sourceforge.net
Cc:     linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, kernel-team@android.com,
        Daniel Rosenberg <drosen@google.com>
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Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Fixes possible underflows when dealing with unusable blocks.

Signed-off-by: Daniel Rosenberg <drosen@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