[PATCH v2] f2fs: fix to avoid mmap vs set_compress_option case

[Chao Yu <chao@kernel.org>]

Compression option in inode should not be changed after they have
been used, however, it may happen in below race case:

Thread A				Thread B
- f2fs_ioc_set_compress_option
 - check f2fs_is_mmap_file()
 - check get_dirty_pages()
 - check F2FS_HAS_BLOCKS()
					- f2fs_file_mmap
					 - set_inode_flag(FI_MMAP_FILE)
					- fault
					 - do_page_mkwrite
					  - f2fs_vm_page_mkwrite
					  - f2fs_get_block_locked
					 - fault_dirty_shared_page
					  - set_page_dirty
 - update i_compress_algorithm
 - update i_log_cluster_size
 - update i_cluster_size

Avoid such race condition by covering f2fs_file_mmap() w/ inode lock,
meanwhile add mmap file check condition in f2fs_may_compress() as well.

Fixes: e1e8debec656 ("f2fs: add F2FS_IOC_SET_COMPRESS_OPTION ioctl")
Signed-off-by: Chao Yu <chao@kernel.org>
---
v2:
- add mmap file check condition in f2fs_may_compress()
 fs/f2fs/f2fs.h |  3 ++-
 fs/f2fs/file.c | 14 +++++++++++---
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 9bd83fb28439..0db8b37c7a4d 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -4487,7 +4487,8 @@ static inline bool f2fs_low_mem_mode(struct f2fs_sb_info *sbi)
 static inline bool f2fs_may_compress(struct inode *inode)
 {
 	if (IS_SWAPFILE(inode) || f2fs_is_pinned_file(inode) ||
-		f2fs_is_atomic_file(inode) || f2fs_has_inline_data(inode))
+		f2fs_is_atomic_file(inode) || f2fs_has_inline_data(inode) ||
+		f2fs_is_mmap_file(inode))
 		return false;
 	return S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode);
 }
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 7b097ab2f5e4..685ded62fc28 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -519,17 +519,25 @@ static loff_t f2fs_llseek(struct file *file, loff_t offset, int whence)
 static int f2fs_file_mmap(struct file *file, struct vm_area_struct *vma)
 {
 	struct inode *inode = file_inode(file);
+	int ret = 0;
 
 	if (unlikely(f2fs_cp_error(F2FS_I_SB(inode))))
 		return -EIO;
 
-	if (!f2fs_is_compress_backend_ready(inode))
-		return -EOPNOTSUPP;
+	inode_lock(inode);
+
+	if (!f2fs_is_compress_backend_ready(inode)) {
+		ret = -EOPNOTSUPP;
+		goto out_unlock;
+	}
 
 	file_accessed(file);
 	vma->vm_ops = &f2fs_file_vm_ops;
 	set_inode_flag(inode, FI_MMAP_FILE);
-	return 0;
+
+out_unlock:
+	inode_unlock(inode);
+	return ret;
 }
 
 static int f2fs_file_open(struct inode *inode, struct file *filp)
-- 
2.40.1