CVE-2024-39463 9p: add missing locking around taking dentry fid list

In the Linux kernel, the following vulnerability has been resolved: 9p: add missing locking around taking dentry fid list Fix a use-after-free on dentry's dfsdata fid list when a thread looks up a fid through dentry while another thread unlinks it: UAF thread: refcountt: addition on 0;...