[PATCH] f2fs: remove race condition in releasing cblocks

From: Daeho Jeong
Date: Fri May 08 2020 - 00:25:14 EST


From: Daeho Jeong <daehojeong@xxxxxxxxxx>

Now, if writing pages and releasing compress blocks occur
simultaneously, and releasing cblocks is executed more than one time
to a file, then total block count of filesystem and block count of the
file could be incorrect and damaged.

We have to execute releasing compress blocks only one time for a file
without being interfered by writepages path.

Signed-off-by: Daeho Jeong <daehojeong@xxxxxxxxxx>
---
fs/f2fs/file.c | 31 ++++++++++++++++++++++++-------
1 file changed, 24 insertions(+), 7 deletions(-)

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 4aab4b42d8ba..a92bc51b9b28 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -3488,6 +3488,7 @@ static int f2fs_release_compress_blocks(struct file *filp, unsigned long arg)
pgoff_t page_idx = 0, last_idx;
unsigned int released_blocks = 0;
int ret;
+ int writecount;

if (!f2fs_sb_has_compression(F2FS_I_SB(inode)))
return -EOPNOTSUPP;
@@ -3509,13 +3510,29 @@ static int f2fs_release_compress_blocks(struct file *filp, unsigned long arg)

inode_lock(inode);

- if (!IS_IMMUTABLE(inode)) {
- F2FS_I(inode)->i_flags |= F2FS_IMMUTABLE_FL;
- f2fs_set_inode_flags(inode);
- inode->i_ctime = current_time(inode);
- f2fs_mark_inode_dirty_sync(inode, true);
+ writecount = atomic_read(&inode->i_writecount);
+ if ((filp->f_mode & FMODE_WRITE && writecount != 1) || writecount) {
+ ret = -EBUSY;
+ goto out;
}

+ if (IS_IMMUTABLE(inode)) {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ ret = filemap_write_and_wait_range(inode->i_mapping, 0, LLONG_MAX);
+ if (ret)
+ goto out;
+
+ if (!F2FS_I(inode)->i_compr_blocks)
+ goto out;
+
+ F2FS_I(inode)->i_flags |= F2FS_IMMUTABLE_FL;
+ f2fs_set_inode_flags(inode);
+ inode->i_ctime = current_time(inode);
+ f2fs_mark_inode_dirty_sync(inode, true);
+
down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
down_write(&F2FS_I(inode)->i_mmap_sem);

@@ -3554,9 +3571,9 @@ static int f2fs_release_compress_blocks(struct file *filp, unsigned long arg)

up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
up_write(&F2FS_I(inode)->i_mmap_sem);
-
- inode_unlock(inode);
out:
+ inode_unlock(inode);
+
mnt_drop_write_file(filp);

if (ret >= 0) {
--
2.26.2.526.g744177e7f7-goog