From 9d96c75bad48308c4bb8d0d815d6a4f2132a4a17 Mon Sep 17 00:00:00 2001
From: mpi <mpi@openbsd.org>
Date: Mon, 22 Aug 2016 10:40:36 +0000
Subject: [PATCH] Call csignal() and selwakeup() from a KERNEL_LOCK'd task.

This will allow us make bpf_tap() KERNEL_LOCK() free.

Discussed with dlg@ and input from guenther@
---
 sys/net/bpf.c     | 29 +++++++++++++++++++++++++----
 sys/net/bpfdesc.h |  6 +++---
 2 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/sys/net/bpf.c b/sys/net/bpf.c
index d731632a2bd..98a367b70c4 100644
--- a/sys/net/bpf.c
+++ b/sys/net/bpf.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: bpf.c,v 1.147 2016/08/15 07:20:14 mpi Exp $	*/
+/*	$OpenBSD: bpf.c,v 1.148 2016/08/22 10:40:36 mpi Exp $	*/
 /*	$NetBSD: bpf.c,v 1.33 1997/02/21 23:59:35 thorpej Exp $	*/
 
 /*
@@ -57,6 +57,8 @@
 #include <sys/atomic.h>
 #include <sys/srp.h>
 #include <sys/specdev.h>
+#include <sys/selinfo.h>
+#include <sys/task.h>
 
 #include <net/if.h>
 #include <net/bpf.h>
@@ -103,6 +105,7 @@ int	bpf_setif(struct bpf_d *, struct ifreq *);
 int	bpfpoll(dev_t, int, struct proc *);
 int	bpfkqfilter(dev_t, struct knote *);
 void	bpf_wakeup(struct bpf_d *);
+void	bpf_wakeup_cb(void *);
 void	bpf_catchpacket(struct bpf_d *, u_char *, size_t, size_t,
 	    void (*)(const void *, void *, size_t), struct timeval *);
 void	bpf_reset_d(struct bpf_d *);
@@ -345,6 +348,7 @@ bpfopen(dev_t dev, int flag, int mode, struct proc *p)
 	bd->bd_unit = unit;
 	bd->bd_bufsize = bpf_bufsize;
 	bd->bd_sig = SIGIO;
+	task_set(&bd->bd_wake_task, bpf_wakeup_cb, bd);
 
 	if (flag & FNONBLOCK)
 		bd->bd_rtout = -1;
@@ -515,12 +519,29 @@ bpfread(dev_t dev, struct uio *uio, int ioflag)
 void
 bpf_wakeup(struct bpf_d *d)
 {
-	wakeup((caddr_t)d);
+	/*
+	 * As long as csignal() and selwakeup() need to be protected
+	 * by the KERNEL_LOCK() we have to delay the wakeup to
+	 * another context to keep the hot path KERNEL_LOCK()-free.
+	 */
+	bpf_get(d);
+	if (!task_add(systq, &d->bd_wake_task))
+		bpf_put(d);
+}
+
+void
+bpf_wakeup_cb(void *xd)
+{
+	struct bpf_d *d = xd;
+
+	KERNEL_ASSERT_LOCKED();
+
+	wakeup(d);
 	if (d->bd_async && d->bd_sig)
-		csignal(d->bd_pgid, d->bd_sig,
-		    d->bd_siguid, d->bd_sigeuid);
+		csignal(d->bd_pgid, d->bd_sig, d->bd_siguid, d->bd_sigeuid);
 
 	selwakeup(&d->bd_sel);
+	bpf_put(d);
 }
 
 int
diff --git a/sys/net/bpfdesc.h b/sys/net/bpfdesc.h
index e5c7cea9172..bb62a371130 100644
--- a/sys/net/bpfdesc.h
+++ b/sys/net/bpfdesc.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: bpfdesc.h,v 1.30 2016/03/30 12:33:10 dlg Exp $	*/
+/*	$OpenBSD: bpfdesc.h,v 1.31 2016/08/22 10:40:36 mpi Exp $	*/
 /*	$NetBSD: bpfdesc.h,v 1.11 1995/09/27 18:30:42 thorpej Exp $	*/
 
 /*
@@ -42,8 +42,6 @@
 
 #ifdef _KERNEL
 
-#include <sys/selinfo.h>
-
 /*
  * Descriptor associated with each open bpf file.
  */
@@ -90,6 +88,8 @@ struct bpf_d {
 	struct selinfo	bd_sel;		/* bsd select info */
 	int		bd_unit;	/* logical unit number */
 	LIST_ENTRY(bpf_d) bd_list;	/* descriptor list */
+
+	struct task	bd_wake_task;	/* delay csignal() and selwakeup() */
 };
 
 /*
-- 
2.20.1