Re: [PATCH v3 net-next 12/14] af_unix: Detect dead SCC.

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Paolo Abeni <pabeni@redhat.com>
Date: Tue, 27 Feb 2024 12:25:56 +0100
> On Fri, 2024-02-23 at 13:40 -0800, Kuniyuki Iwashima wrote:
> > When iterating SCC, we call unix_vertex_dead() for each vertex
> > to check if the vertex is close()d and has no bridge to another
> > SCC.
> > 
> > If both conditions are true for every vertex in SCC, we can
> > execute garbage collection for all skb in the SCC.
> > 
> > The actual garbage collection is done in the following patch,
> > replacing the old implementation.
> > 
> > Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> > ---
> >  net/unix/garbage.c | 37 ++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 36 insertions(+), 1 deletion(-)
> > 
> > diff --git a/net/unix/garbage.c b/net/unix/garbage.c
> > index 0eb1610c96d7..060e81be3614 100644
> > --- a/net/unix/garbage.c
> > +++ b/net/unix/garbage.c
> > @@ -288,6 +288,32 @@ void unix_destroy_fpl(struct scm_fp_list *fpl)
> >  	unix_free_vertices(fpl);
> >  }
> >  
> > +static bool unix_vertex_dead(struct unix_vertex *vertex)
> > +{
> > +	struct unix_edge *edge;
> > +	struct unix_sock *u;
> > +	long total_ref;
> > +
> > +	list_for_each_entry(edge, &vertex->edges, vertex_entry) {
> > +		struct unix_vertex *next_vertex = unix_edge_successor(edge);
> > +
> > +		if (!next_vertex)
> > +			return false;
> > +
> > +		if (next_vertex->scc_index != vertex->scc_index)
> > +			return false;
> > +	}
> > +
> > +	edge = list_first_entry(&vertex->edges, typeof(*edge), vertex_entry);
> > +	u = edge->predecessor;
> > +	total_ref = file_count(u->sk.sk_socket->file);
> > +
> > +	if (total_ref != vertex->out_degree)
> > +		return false;
> > +
> > +	return true;
> > +}
> > +
> >  static bool unix_scc_cyclic(struct list_head *scc)
> >  {
> >  	struct unix_vertex *vertex;
> > @@ -350,6 +376,7 @@ static void __unix_walk_scc(struct unix_vertex *vertex)
> >  
> >  	if (vertex->index == vertex->scc_index) {
> >  		struct list_head scc;
> > +		bool dead = true;
> 
> Very minor nit: the above variable 'sounds' alike referring to the
> current vertex, while instead it tracks a global status, what about
> 'all_dead' or 'gc_all'?

Exactly. I'll use scc_dead or gc_scc to be consistent
with unix_vertex_dead().

Thanks!