[src/trunk]: src/sys/net Add a locking notes for if_spppsubr

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

details:   https://anonhg.NetBSD.org/src/rev/6edbb21feab3
branches:  trunk
changeset: 827085:6edbb21feab3
user:      knakahara <knakahara%NetBSD.org@localhost>
date:      Thu Oct 12 09:53:55 2017 +0000

description:
Add a locking notes for if_spppsubr

diffstat:

 sys/net/if_spppvar.h |  23 ++++++++++++++++++++++-
 1 files changed, 22 insertions(+), 1 deletions(-)

diffs (35 lines):

diff -r 9a6d50b38ed7 -r 6edbb21feab3 sys/net/if_spppvar.h
--- a/sys/net/if_spppvar.h      Thu Oct 12 09:50:55 2017 +0000
+++ b/sys/net/if_spppvar.h      Thu Oct 12 09:53:55 2017 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: if_spppvar.h,v 1.21 2017/10/12 09:49:43 knakahara Exp $        */
+/*     $NetBSD: if_spppvar.h,v 1.22 2017/10/12 09:53:55 knakahara Exp $        */
 
 #ifndef _NET_IF_SPPPVAR_H_
 #define _NET_IF_SPPPVAR_H_
@@ -182,4 +182,25 @@
 int sppp_isempty (struct ifnet *);
 void sppp_flush (struct ifnet *);
 #endif
+
+/*
+ * Locking notes:
+ * + spppq is protected by spppq_lock (an adaptive mutex)
+ *     spppq is a list of all struct sppps, and it is used for
+ *     sending keepalive packets.
+ * + struct sppp is protected by sppp->pp_lock (an rwlock)
+ *     sppp holds configuration parameters for line,
+ *     authentication and addresses. It also has pointers
+ *     of functions to notify events to lower layer.
+ *     When notify events, sppp->pp_lock must be released.
+ *     Because the event handler implemented in a lower
+ *     layer often call functions implemented in
+ *     if_spppsubr.c.
+ *
+ * Locking order:
+ *    - spppq_lock => struct sppp->pp_lock
+ *
+ * NOTICE
+ * - Lower layers must not acquire sppp->pp_lock
+ */
 #endif /* !_NET_IF_SPPPVAR_H_ */