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 torvalds#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.

Fixes: 7eb5b3e ("netfs, fscache: Move /proc/fs/fscache to /proc/fs/netfs and put in a symlink")
Cc: stable@kernel.org
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Link: https://lore.kernel.org/r/20240826113404.3214786-1-libaokun@huaweicloud.com
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/netfs/main.c

@@ -142,7 +142,7 @@ static int __init netfs_init(void)
 
 error_fscache:
 error_procfile:
-	remove_proc_entry("fs/netfs", NULL);
+	remove_proc_subtree("fs/netfs", NULL);
 error_proc:
 	mempool_exit(&netfs_subrequest_pool);
 error_subreqpool:
@@ -159,7 +159,7 @@ fs_initcall(netfs_init);
 static void __exit netfs_exit(void)
 {
 	fscache_exit();
-	remove_proc_entry("fs/netfs", NULL);
+	remove_proc_subtree("fs/netfs", NULL);
 	mempool_exit(&netfs_subrequest_pool);
 	kmem_cache_destroy(netfs_subrequest_slab);
 	mempool_exit(&netfs_request_pool);