[src/trunk]: src/sys/kern threadpool(9): Make threadpool_percpu_ref_remote no...

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

details:   https://anonhg.NetBSD.org/src/rev/621f22b8f5fe
branches:  trunk
changeset: 949406:621f22b8f5fe
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Wed Jan 13 02:19:08 2021 +0000

description:
threadpool(9): Make threadpool_percpu_ref_remote non-sleepable.

Needed for threadpool-based workqueue_enqueue to run in interrupt
context.

diffstat:

 sys/kern/kern_threadpool.c |  14 ++++++++++----
 1 files changed, 10 insertions(+), 4 deletions(-)

diffs (37 lines):

diff -r 39108dce72dc -r 621f22b8f5fe sys/kern/kern_threadpool.c
--- a/sys/kern/kern_threadpool.c        Tue Jan 12 21:48:10 2021 +0000
+++ b/sys/kern/kern_threadpool.c        Wed Jan 13 02:19:08 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: kern_threadpool.c,v 1.19 2020/09/07 01:08:27 riastradh Exp $   */
+/*     $NetBSD: kern_threadpool.c,v 1.20 2021/01/13 02:19:08 riastradh Exp $   */
 
 /*-
  * Copyright (c) 2014, 2018 The NetBSD Foundation, Inc.
@@ -81,7 +81,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_threadpool.c,v 1.19 2020/09/07 01:08:27 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_threadpool.c,v 1.20 2021/01/13 02:19:08 riastradh Exp $");
 
 #include <sys/types.h>
 #include <sys/param.h>
@@ -644,10 +644,16 @@
 {
        struct threadpool **poolp, *pool;
 
-       percpu_traverse_enter();
+       /*
+        * As long as xcalls are blocked -- e.g., by kpreempt_disable
+        * -- the percpu object will not be swapped and destroyed.  We
+        * can't write to it, because the data may have already been
+        * moved to a new buffer, but we can safely read from it.
+        */
+       kpreempt_disable();
        poolp = percpu_getptr_remote(pool_percpu->tpp_percpu, ci);
        pool = *poolp;
-       percpu_traverse_exit();
+       kpreempt_enable();
 
        return pool;
 }