Re: [RFC PATCH net] net: Work around lockdep limitation in sockets that use sockets

From: David Miller
Date: Thu Mar 09 2017 - 02:29:48 EST

From: David Howells <dhowells@xxxxxxxxxx>
Date: Mon, 06 Mar 2017 15:04:44 +0000

> Fix the general case by:
> (1) Double up all the locking keys used in sockets so that one set are
> used if the socket is created by userspace and the other set is used
> if the socket is created by the kernel.
> (2) Store the kern parameter passed to sk_alloc() in a variable in the
> sock struct (sk_kern_sock). This informs sock_lock_init(),
> sock_init_data() and sk_clone_lock() as to the lock keys to be used.
> Note that the child created by sk_clone_lock() inherits the parent's
> kern setting.
> (3) Add a 'kern' parameter to ->accept() that is analogous to the one
> passed in to ->create() that distinguishes whether kernel_accept() or
> sys_accept4() was the caller and can be passed to sk_alloc().
> Note that a lot of accept functions merely dequeue an already
> allocated socket. I haven't touched these as the new socket already
> exists before we get the parameter.
> Note also that there are a couple of places where I've made the accepted
> socket unconditionally kernel-based:
> irda_accept()
> rds_rcp_accept_one()
> tcp_accept_from_sock()
> because they follow a sock_create_kern() and accept off of that.

I guess this is fine, but I think you can use one of the two "sk_padding"
bits in struct sock instead of making the structure larger.