netfs: Delete subtree of 'fs/netfs' when netfs module exits

In the Linux kernel, the following vulnerability has been resolved:

netfs: Delete subtree of 'fs/netfs' when netfs module exits

In netfs_init() or fscache_proc_init(), we create dentry under 'fs/netfs',

but in netfs_exit(), we only delete the proc entry of 'fs/netfs' without

deleting its subtree. This triggers the following WARNING:

==================================================================

remove_proc_entry: removing non-empty directory 'fs/netfs', leaking at least 'requests'

WARNING: CPU: 4 PID: 566 at fs/proc/generic.c:717 remove_proc_entry+0x160/0x1c0

Modules linked in: netfs(-)

CPU: 4 UID: 0 PID: 566 Comm: rmmod Not tainted 6.11.0-rc3 #860

RIP: 0010:remove_proc_entry+0x160/0x1c0

Call Trace:

<TASK>

netfs_exit+0x12/0x620 [netfs]

__do_sys_delete_module.isra.0+0x14c/0x2e0

do_syscall_64+0x4b/0x110

entry_SYSCALL_64_after_hwframe+0x76/0x7e

==================================================================

Therefore use remove_proc_subtree() instead of remove_proc_entry() to

fix the above problem.