From: Tahsin Erdogan tahsin@google.com
[ Upstream commit 407cd7fb83c0ebabb490190e673d8c71ee7df97e ]
ext4_inode_info->i_data is the storage area for 4 types of data:
a) Extents data b) Inline data c) Block map d) Fast symlink data (symlink length < 60)
Extents data case is positively identified by EXT4_INODE_EXTENTS flag. Inline data case is also obvious because of EXT4_INODE_INLINE_DATA flag.
Distinguishing c) and d) however requires additional logic. This currently relies on i_blocks count. After subtracting external xattr block from i_blocks, if it is greater than 0 then we know that some data blocks exist, so there must be a block map.
This logic got broken after ea_inode feature was added. That feature charges the data blocks of external xattr inodes to the referencing inode and so adds them to the i_blocks. To fix this, we could subtract ea_inode blocks by iterating through all xattr entries and then check whether remaining i_blocks count is zero. Besides being complicated, this won't change the fact that the current way of distinguishing between c) and d) is fragile.
The alternative solution is to test whether i_size is less than 60 to determine fast symlink case. ext4_symlink() uses the same test to decide whether to store the symlink in i_data. There is one caveat to address before this can work though.
If an inode's i_nlink is zero during eviction, its i_size is set to zero and its data is truncated. If system crashes before inode is removed from the orphan list, next boot orphan cleanup may find the inode with zero i_size. So, a symlink that had its data stored in a block may now appear to be a fast symlink. The solution used in this patch is to treat i_size = 0 as a non-fast symlink case. A zero sized symlink is not legal so the only time this can happen is the mentioned scenario. This is also logically correct because a i_size = 0 symlink has no data stored in i_data.
Suggested-by: Andreas Dilger adilger@dilger.ca Signed-off-by: Tahsin Erdogan tahsin@google.com Signed-off-by: Theodore Ts'o tytso@mit.edu Reviewed-by: Andreas Dilger adilger@dilger.ca Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- fs/ext4/inode.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-)
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index c2434d72681e..c70d7d3832c4 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -140,16 +140,12 @@ static int ext4_meta_trans_blocks(struct inode *inode, int lblocks,
/* * Test whether an inode is a fast symlink. + * A fast symlink has its symlink data stored in ext4_inode_info->i_data. */ static int ext4_inode_is_fast_symlink(struct inode *inode) { - int ea_blocks = EXT4_I(inode)->i_file_acl ? - EXT4_CLUSTER_SIZE(inode->i_sb) >> 9 : 0; - - if (ext4_has_inline_data(inode)) - return 0; - - return (S_ISLNK(inode->i_mode) && inode->i_blocks - ea_blocks == 0); + return S_ISLNK(inode->i_mode) && inode->i_size && + (inode->i_size < EXT4_N_BLOCKS * 4); }
/* @@ -253,6 +249,16 @@ void ext4_evict_inode(struct inode *inode)
if (IS_SYNC(inode)) ext4_handle_sync(handle); + + /* + * Set inode->i_size to 0 before calling ext4_truncate(). We need + * special handling of symlinks here because i_size is used to + * determine whether ext4_inode_info->i_data contains symlink data or + * block mappings. Setting i_size to 0 will remove its fast symlink + * status. Erase i_data so that it becomes a valid empty block map. + */ + if (ext4_inode_is_fast_symlink(inode)) + memset(EXT4_I(inode)->i_data, 0, sizeof(EXT4_I(inode)->i_data)); inode->i_size = 0; err = ext4_mark_inode_dirty(handle, inode); if (err) {