f2fs: synchronize atomic write aborts

To fix a race condition between atomic write aborts, I use the inode
lock and make COW inode to be re-usable thoroughout the whole
atomic file inode lifetime.

Reported-by: syzbot+823000d23b3400619f7c@syzkaller.appspotmail.com
Fixes: 3db1de0e582c ("f2fs: change the current atomic write way")
Signed-off-by: Daeho Jeong <daehojeong@google.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

1 files changed, 29 insertions, 15 deletions

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 300eae8b5415..6436c52e7913 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -1863,7 +1863,10 @@ static int f2fs_release_file(struct inode *inode, struct file *filp)
 			atomic_read(&inode->i_writecount) != 1)
 		return 0;
 
+	inode_lock(inode);
 	f2fs_abort_atomic_write(inode, true);
+	inode_unlock(inode);
+
 	return 0;
 }
 
@@ -1878,8 +1881,12 @@ static int f2fs_file_flush(struct file *file, fl_owner_t id)
 	 * before dropping file lock, it needs to do in ->flush.
 	 */
 	if (F2FS_I(inode)->atomic_write_task == current &&
-				(current->flags & PF_EXITING))
+				(current->flags & PF_EXITING)) {
+		inode_lock(inode);
 		f2fs_abort_atomic_write(inode, true);
+		inode_unlock(inode);
+	}
+
 	return 0;
 }
 
@@ -2085,19 +2092,28 @@ static int f2fs_ioc_start_atomic_write(struct file *filp, bool truncate)
 		goto out;
 	}
 
-	/* Create a COW inode for atomic write */
-	pinode = f2fs_iget(inode->i_sb, fi->i_pino);
-	if (IS_ERR(pinode)) {
-		f2fs_up_write(&fi->i_gc_rwsem[WRITE]);
-		ret = PTR_ERR(pinode);
-		goto out;
-	}
+	/* Check if the inode already has a COW inode */
+	if (fi->cow_inode == NULL) {
+		/* Create a COW inode for atomic write */
+		pinode = f2fs_iget(inode->i_sb, fi->i_pino);
+		if (IS_ERR(pinode)) {
+			f2fs_up_write(&fi->i_gc_rwsem[WRITE]);
+			ret = PTR_ERR(pinode);
+			goto out;
+		}
 
-	ret = f2fs_get_tmpfile(mnt_userns, pinode, &fi->cow_inode);
-	iput(pinode);
-	if (ret) {
-		f2fs_up_write(&fi->i_gc_rwsem[WRITE]);
-		goto out;
+		ret = f2fs_get_tmpfile(mnt_userns, pinode, &fi->cow_inode);
+		iput(pinode);
+		if (ret) {
+			f2fs_up_write(&fi->i_gc_rwsem[WRITE]);
+			goto out;
+		}
+
+		set_inode_flag(fi->cow_inode, FI_COW_FILE);
+		clear_inode_flag(fi->cow_inode, FI_INLINE_DATA);
+	} else {
+		/* Reuse the already created COW inode */
+		f2fs_do_truncate_blocks(fi->cow_inode, 0, true);
 	}
 
 	f2fs_write_inode(inode, NULL);
@@ -2105,8 +2121,6 @@ static int f2fs_ioc_start_atomic_write(struct file *filp, bool truncate)
 	stat_inc_atomic_inode(inode);
 
 	set_inode_flag(inode, FI_ATOMIC_FILE);
-	set_inode_flag(fi->cow_inode, FI_COW_FILE);
-	clear_inode_flag(fi->cow_inode, FI_INLINE_DATA);
 
 	isize = i_size_read(inode);
 	fi->original_i_size = isize;