From: mvs <mvs@openbsd.org>
Date: Tue, 18 Apr 2023 22:00:19 +0000 (+0000)
Subject: Document `ifnetlist' locking.
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=a6b8260995b7cce5f7c2b4922e0b7f1c61321c01;p=openbsd

Document `ifnetlist' locking.

We use both kernel and net lock for protect `ifnetlist'. This means we
do modification with both locks held, but for read-only access only one
lock required. Some places doing `ifnetlist' foreach loop are protected
by kernel lock and context switch can't be introduced there. This is the
exception, so "XXXSMP:" comment added.

Proposed and ok by bluhm@
---

diff --git a/sys/net/if.c b/sys/net/if.c
index e4675704a3b..1cd91f8fa80 100644
--- a/sys/net/if.c
+++ b/sys/net/if.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: if.c,v 1.688 2023/04/08 13:49:38 mvs Exp $	*/
+/*	$OpenBSD: if.c,v 1.689 2023/04/18 22:00:19 mvs Exp $	*/
 /*	$NetBSD: if.c,v 1.35 1996/05/07 05:26:04 thorpej Exp $	*/
 
 /*
@@ -272,6 +272,10 @@ ifinit(void)
 
 static struct if_idxmap if_idxmap;
 
+/*
+ * XXXSMP: For `ifnetlist' modification both kernel and net locks
+ * should be taken. For read-only access only one lock of them required.
+ */
 struct ifnet_head ifnetlist = TAILQ_HEAD_INITIALIZER(ifnetlist);
 
 static inline unsigned int
diff --git a/sys/net/if_var.h b/sys/net/if_var.h
index 49b38eaf797..0eeebdc9bbb 100644
--- a/sys/net/if_var.h
+++ b/sys/net/if_var.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: if_var.h,v 1.123 2023/04/05 19:35:23 bluhm Exp $	*/
+/*	$OpenBSD: if_var.h,v 1.124 2023/04/18 22:00:19 mvs Exp $	*/
 /*	$NetBSD: if.h,v 1.23 1996/05/07 02:40:27 thorpej Exp $	*/
 
 /*
@@ -121,7 +121,7 @@ TAILQ_HEAD(ifnet_head, ifnet);		/* the actual queue head */
 struct ifnet {				/* and the entries */
 	void	*if_softc;		/* [I] lower-level data for this if */
 	struct	refcnt if_refcnt;
-	TAILQ_ENTRY(ifnet) if_list;	/* [K] all struct ifnets are chained */
+	TAILQ_ENTRY(ifnet) if_list;	/* [NK] all struct ifnets are chained */
 	TAILQ_HEAD(, ifaddr) if_addrlist; /* [N] list of addresses per if */
 	TAILQ_HEAD(, ifmaddr) if_maddrlist; /* [N] list of multicast records */
 	TAILQ_HEAD(, ifg_list) if_groups; /* [N] list of groups per if */