[src/trunk]: src/sys/kern Fix callout-skew source so it runs only when needed...

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

details:   https://anonhg.NetBSD.org/src/rev/3a29714b9ede
branches:  trunk
changeset: 342613:3a29714b9ede
user:      tls <tls%NetBSD.org@localhost>
date:      Fri Jan 01 16:09:00 2016 +0000

description:
Fix callout-skew source so it runs only when needed (remove second callout,
eliminate race).

diffstat:

 sys/kern/kern_rndq.c |  33 ++++++++++++---------------------
 1 files changed, 12 insertions(+), 21 deletions(-)

diffs (98 lines):

diff -r fc0121a3f1ca -r 3a29714b9ede sys/kern/kern_rndq.c
--- a/sys/kern/kern_rndq.c      Fri Jan 01 15:18:39 2016 +0000
+++ b/sys/kern/kern_rndq.c      Fri Jan 01 16:09:00 2016 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: kern_rndq.c,v 1.73 2015/08/29 10:00:19 mlelstv Exp $   */
+/*     $NetBSD: kern_rndq.c,v 1.74 2016/01/01 16:09:00 tls Exp $       */
 
 /*-
  * Copyright (c) 1997-2013 The NetBSD Foundation, Inc.
@@ -32,7 +32,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_rndq.c,v 1.73 2015/08/29 10:00:19 mlelstv Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_rndq.c,v 1.74 2016/01/01 16:09:00 tls Exp $");
 
 #include <sys/param.h>
 #include <sys/atomic.h>
@@ -407,8 +407,8 @@
 #if defined(__HAVE_CPU_COUNTER)
 static struct {
        kmutex_t        lock;
+       int             iter;
        struct callout  callout;
-       struct callout  stop_callout;
        krndsource_t    source;
 } rnd_skew __cacheline_aligned;
 
@@ -426,21 +426,14 @@
 }
 
 static void
-rnd_skew_stop_intr(void *arg)
-{
-
-       callout_stop(&rnd_skew.callout);
-}
-
-static void
 rnd_skew_get(size_t bytes, void *priv)
 {
        krndsource_t *skewsrcp = priv;
 
        KASSERT(skewsrcp == &rnd_skew.source);
        if (RND_ENABLED(skewsrcp)) {
-               /* Measure for 30s */
-               callout_schedule(&rnd_skew.stop_callout, hz * 30);
+               /* Measure 100 times */
+               rnd_skew.iter = 100;
                callout_schedule(&rnd_skew.callout, 1);
        }
 }
@@ -448,8 +441,6 @@
 static void
 rnd_skew_intr(void *arg)
 {
-       static int flipflop;
-
        /*
         * Even on systems with seemingly stable clocks, the
         * delta-time entropy estimator seems to think we get 1 bit here
@@ -457,14 +448,15 @@
         *
         */
        mutex_spin_enter(&rnd_skew.lock);
-       flipflop = !flipflop;
 
        if (RND_ENABLED(&rnd_skew.source)) {
-               if (flipflop) {
+               int next_ticks = 1;
+               if (rnd_skew.iter & 1) {
                        rnd_add_uint32(&rnd_skew.source, rnd_counter());
-                       callout_schedule(&rnd_skew.callout, hz / 10);
-               } else {
-                       callout_schedule(&rnd_skew.callout, 1);
+                       next_ticks = hz / 10;
+               }
+               if (--rnd_skew.iter > 0) {
+                       callout_schedule(&rnd_skew.callout, next_ticks);
                }
        }
        mutex_spin_exit(&rnd_skew.lock);
@@ -559,14 +551,13 @@
        /* IPL_VM because taken while rnd_global.lock is held.  */
        mutex_init(&rnd_skew.lock, MUTEX_DEFAULT, IPL_VM);
        callout_init(&rnd_skew.callout, CALLOUT_MPSAFE);
-       callout_init(&rnd_skew.stop_callout, CALLOUT_MPSAFE);
        callout_setfunc(&rnd_skew.callout, rnd_skew_intr, NULL);
-       callout_setfunc(&rnd_skew.stop_callout, rnd_skew_stop_intr, NULL);
        rndsource_setcb(&rnd_skew.source, rnd_skew_get, &rnd_skew.source);
        rndsource_setenable(&rnd_skew.source, rnd_skew_enable);
        rnd_attach_source(&rnd_skew.source, "callout", RND_TYPE_SKEW,
            RND_FLAG_COLLECT_VALUE|RND_FLAG_ESTIMATE_VALUE|
            RND_FLAG_HASCB|RND_FLAG_HASENABLE);
+       rnd_skew.iter = 100;
        rnd_skew_intr(NULL);
 #endif