[src/trunk]: src/sys/kern entropy(9): Call entropy_softintr while bound to CPU.

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

details:   https://anonhg.NetBSD.org/src/rev/122a7a91a27c
branches:  trunk
changeset: 364433:122a7a91a27c
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Thu Mar 24 12:58:56 2022 +0000

description:
entropy(9): Call entropy_softintr while bound to CPU.

It looks like We tripped on the new assertion in entropy_account_cpu
when there was pending entropy on cpu0 running lwp0 when xc_broadcast
ran -- since xc_broadcast calls the function directly rather than
calling it through softint_schedule, it's not called via the softint
lwp which would satisfy the assertion.

diffstat:

 sys/kern/kern_entropy.c |  16 ++++++++++++++--
 1 files changed, 14 insertions(+), 2 deletions(-)

diffs (39 lines):

diff -r a9b566a8576b -r 122a7a91a27c sys/kern/kern_entropy.c
--- a/sys/kern/kern_entropy.c   Thu Mar 24 12:12:00 2022 +0000
+++ b/sys/kern/kern_entropy.c   Thu Mar 24 12:58:56 2022 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: kern_entropy.c,v 1.53 2022/03/23 23:20:52 riastradh Exp $      */
+/*     $NetBSD: kern_entropy.c,v 1.54 2022/03/24 12:58:56 riastradh Exp $      */
 
 /*-
  * Copyright (c) 2019 The NetBSD Foundation, Inc.
@@ -75,7 +75,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_entropy.c,v 1.53 2022/03/23 23:20:52 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_entropy.c,v 1.54 2022/03/24 12:58:56 riastradh Exp $");
 
 #include <sys/param.h>
 #include <sys/types.h>
@@ -413,8 +413,20 @@
 static void
 entropy_init_late_cpu(void *a, void *b)
 {
+       int bound;
 
+       /*
+        * We're not necessarily in a softint lwp here (xc_broadcast
+        * triggers softint on other CPUs, but calls directly on this
+        * CPU), so explicitly bind to the current CPU to invoke the
+        * softintr -- this lets us have a simpler assertion in
+        * entropy_account_cpu.  Not necessary to avoid migration
+        * because xc_broadcast disables kpreemption anyway, but it
+        * doesn't hurt.
+        */
+       bound = curlwp_bind();
        entropy_softintr(NULL);
+       curlwp_bindx(bound);
 }
 
 /*