f2fs: set ->owner for debugfs status file's file_operations

The struct file_operations instance serving the f2fs/status debugfs file lacks an initialization of its ->owner.

This means that although that file might have been opened, the f2fs module can still get removed. Any further operation on that opened file, releasing included, will cause accesses to unmapped memory.

Indeed, Mike Marshall reported the following:

  BUG: unable to handle kernel paging request at ffffffffa0307430
  IP: [<ffffffff8132a224>] full_proxy_release+0x24/0x90
  <...>
  Call Trace:
   [] __fput+0xdf/0x1d0
   [] ____fput+0xe/0x10
   [] task_work_run+0x8e/0xc0
   [] do_exit+0x2ae/0xae0
   [] ? __audit_syscall_entry+0xae/0x100
   [] ? syscall_trace_enter+0x1ca/0x310
   [] do_group_exit+0x44/0xc0
   [] SyS_exit_group+0x14/0x20
   [] do_syscall_64+0x61/0x150
   [] entry_SYSCALL64_slow_path+0x25/0x25
  <...>
  ---[ end trace f22ae883fa3ea6b8 ]---
  Fixing recursive fault but reboot is needed!

Fix this by initializing the f2fs/status file_operations' ->owner with THIS_MODULE.

This will allow debugfs to grab a reference to the f2fs module upon any open on that file, thus preventing it from getting removed.

---
Applicable to next-20161117. Compile-only tested.

 fs/f2fs/debug.c | 1 +
 1 file changed, 1 insertion(+)

index 2fdf233..678733c 100644
@@ -376,6 +376,7 @@ static int stat_open(struct inode *inode, struct file *file)
 }
 
 static const struct file_operations stat_fops = {
+	.owner = THIS_MODULE,
 	.open = stat_open,
 	.read = seq_read,
 	.llseek = seq_lseek,

2.10.2