ksmbd: vfs: fix race on m_flags in vfs_cache

ksmbd: vfs: fix race on m_flags in vfs_cache

ksmbd maintains delete-on-close and pending-delete state in
ksmbd_inode->m_flags. In vfs_cache.c this field is accessed under
inconsistent locking: some paths read and modify m_flags under
ci->m_lock while others do so without taking the lock at all.

Examples:

 - ksmbd_query_inode_status() and __ksmbd_inode_close() use
   ci->m_lock when checking or updating m_flags.
 - ksmbd_inode_pending_delete(), ksmbd_set_inode_pending_delete(),
   ksmbd_clear_inode_pending_delete() and ksmbd_fd_set_delete_on_close()
   used to read and modify m_flags without ci->m_lock.

This creates a potential data race on m_flags when multiple threads
open, close and delete the same file concurrently. In the worst case
delete-on-close and pending-delete bits can be lost or observed in an
inconsistent state, leading to confusing delete semantics (files that
stay on disk after delete-on-close, or files that disappear while still
in use).

Fix it by:

 - Making ksmbd_query_inode_status() look at m_flags under ci->m_lock
   after dropping inode_hash_lock.
 - Adding ci->m_lock protection to all helpers that read or modify
   m_flags (ksmbd_inode_pending_delete(), ksmbd_set_inode_pending_delete(),
   ksmbd_clear_inode_pending_delete(), ksmbd_fd_set_delete_on_close()).
 - Keeping the existing ci->m_lock protection in __ksmbd_inode_close(),
   and moving the actual unlink/xattr removal outside the lock.

This unifies the locking around m_flags and removes the data race while
preserving the existing delete-on-close behaviour.

Reported-by: Qianchang Zhao <pioooooooooip@gmail.com>
Reported-by: Zhitong Liu <liuzhitong1993@gmail.com>
Signed-off-by: Qianchang Zhao <pioooooooooip@gmail.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>