[src/trunk]: src/sys/net wg: Drop wgp_lock while waiting for endpoint psref t...

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/4ec75222f0bc
branches:  trunk
changeset: 938455:4ec75222f0bc
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Tue Sep 08 16:39:57 2020 +0000

description:
wg: Drop wgp_lock while waiting for endpoint psref to drain.

- This is safe because wgp_endpoint_changing locks out any attempts
  to change the endpoint until the draining is complete.

- This is necessary to avoid a deadlock where the handshake thread
  holds a psref and awaits mutex_enter(wgp->wgp_lock).

XXX The same deadlock may occur in wg_destroy_session.  Not clear
that it's safe to just release wgp_lock there; may need to create a
new session state, say WGS_STATE_DRAINING, while we wait for
psref_target_destroy.  But this needs a little more thought; a new
state may not be necessary, and would be nice to avoid if not
necessary.

diffstat:

 sys/net/if_wg.c |  6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diffs (31 lines):

diff -r bbacbe47c519 -r 4ec75222f0bc sys/net/if_wg.c
--- a/sys/net/if_wg.c   Tue Sep 08 16:39:36 2020 +0000
+++ b/sys/net/if_wg.c   Tue Sep 08 16:39:57 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: if_wg.c,v 1.55 2020/09/07 01:15:25 riastradh Exp $     */
+/*     $NetBSD: if_wg.c,v 1.56 2020/09/08 16:39:57 riastradh Exp $     */
 
 /*
  * Copyright (C) Ryota Ozaki <ozaki.ryota%gmail.com@localhost>
@@ -41,7 +41,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: if_wg.c,v 1.55 2020/09/07 01:15:25 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: if_wg.c,v 1.56 2020/09/08 16:39:57 riastradh Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_inet.h"
@@ -2965,10 +2965,12 @@
 
        if (atomic_load_relaxed(&wgp->wgp_endpoint_changing)) {
                pserialize_perform(wgp->wgp_psz);
+               mutex_exit(wgp->wgp_lock);
                psref_target_destroy(&wgp->wgp_endpoint0->wgsa_psref,
                    wg_psref_class);
                psref_target_init(&wgp->wgp_endpoint0->wgsa_psref,
                    wg_psref_class);
+               mutex_enter(wgp->wgp_lock);
                atomic_store_release(&wgp->wgp_endpoint_changing, 0);
        }
 }