Re: [PATCH 0/1] ns: introduce proc_get_ns_by_fd()

On 09/29, Eric W. Biederman wrote:

Oleg Nesterov [off-list ref] writes:

quoted

OK, I won't insist, this too looks better to me than proc_ns_fdget(&fd_ref).

And in any case fcheck_files() makes more sense than fdget(), somehow I did
not think about this when I sent 1/1.

Hmm. and after the quick look at cleanup_net() I can't understand whether
get_net_ns_by_fd() can use ns_by_fd_rcu() + maybe_get_net(to_net_ns()) or
not... Can it?

Some of those places need a reference that allows them to sleep, and the
code is shared with the legacy pid case so with an addition of get_net
we can use ns_by_fd_rcu().   There are cases like setns that could
use ns_by_fd_rcu() with code reording.

We can implement get_net_ns_by_fd as:
struct net *get_net_ns_by_fd(int fd)
{
        struct net *net;

	rcu_read_lock();
	net = net_ns_by_fd_rcu(fd);
        if (!IS_ERR(net))
        	get_net(net);
        rcu_read_unlock();

	return net;
}

Which means we can achieve code sharing with the pure rcu version
as a base.

Yes, this is what I meant... but don't we need maybe_get_net() ?

Oleg.