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@

diff --git a/sys/net/bpf.c b/sys/net/bpf.c
index d731632..98a367b 100644 (file)
--- 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 e5c7cea..bb62a37 100644 (file)
--- 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() */
 };
 
 /*