[src/trunk]: src/sys/kern Avoid calling entropy_pending() with E->lock held.

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

details:   https://anonhg.NetBSD.org/src/rev/88151ccd0543
branches:  trunk
changeset: 931795:88151ccd0543
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Thu Apr 30 16:43:12 2020 +0000

description:
Avoid calling entropy_pending() with E->lock held.

This is part I of avoiding percpu_foreach with spin lock held.

diffstat:

 sys/kern/kern_entropy.c |  40 +++++++++++++++++++++-------------------
 1 files changed, 21 insertions(+), 19 deletions(-)

diffs (75 lines):

diff -r 49d0e342a030 -r 88151ccd0543 sys/kern/kern_entropy.c
--- a/sys/kern/kern_entropy.c   Thu Apr 30 15:12:25 2020 +0000
+++ b/sys/kern/kern_entropy.c   Thu Apr 30 16:43:12 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: kern_entropy.c,v 1.2 2020/04/30 03:42:23 riastradh Exp $       */
+/*     $NetBSD: kern_entropy.c,v 1.3 2020/04/30 16:43:12 riastradh Exp $       */
 
 /*-
  * Copyright (c) 2019 The NetBSD Foundation, Inc.
@@ -77,7 +77,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_entropy.c,v 1.2 2020/04/30 03:42:23 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_entropy.c,v 1.3 2020/04/30 16:43:12 riastradh Exp $");
 
 #include <sys/param.h>
 #include <sys/types.h>
@@ -932,29 +932,32 @@
 static void
 entropy_thread(void *cookie)
 {
+       bool consolidate;
 
        for (;;) {
                /*
-                * Wait until someone wants to consolidate or there's
-                * full entropy somewhere among the CPUs, as confirmed
-                * at most once per minute.
+                * Wait until there's full entropy somewhere among the
+                * CPUs, as confirmed at most once per minute, or
+                * someone wants to consolidate.
                 */
-               mutex_enter(&E->lock);
-               for (;;) {
-                       if (E->consolidate ||
-                           entropy_pending() >= ENTROPY_CAPACITY*NBBY) {
-                               E->consolidate = false;
-                               break;
-                       }
-                       cv_timedwait(&E->cv, &E->lock, 60*hz);
+               if (entropy_pending() >= ENTROPY_CAPACITY*NBBY) {
+                       consolidate = true;
+               } else {
+                       mutex_enter(&E->lock);
+                       if (!E->consolidate)
+                               cv_timedwait(&E->cv, &E->lock, 60*hz);
+                       consolidate = E->consolidate;
+                       E->consolidate = false;
+                       mutex_exit(&E->lock);
                }
-               mutex_exit(&E->lock);
 
-               /* Do it.  */
-               entropy_consolidate();
+               if (consolidate) {
+                       /* Do it.  */
+                       entropy_consolidate();
 
-               /* Mitigate abuse.  */
-               kpause("entropy", false, hz, NULL);
+                       /* Mitigate abuse.  */
+                       kpause("entropy", false, hz, NULL);
+               }
        }
 }
 
@@ -969,7 +972,6 @@
        uint32_t pending = 0;
 
        percpu_foreach(entropy_percpu, &entropy_pending_cpu, &pending);
-
        return pending;
 }