[src/trunk]: src/sys/kern Rather than calling xc_barrier() in lwp_dtor(), set...

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

details:   https://anonhg.NetBSD.org/src/rev/f2a523effa0b
branches:  trunk
changeset: 1029105:f2a523effa0b
user:      thorpej <thorpej%NetBSD.org@localhost>
date:      Tue Dec 21 19:00:37 2021 +0000

description:
Rather than calling xc_barrier() in lwp_dtor(), set a pre-destruct hook
on the lwp_cache and invoke the barrier there.

diffstat:

 sys/kern/kern_lwp.c |  32 ++++++++++++++++++++------------
 1 files changed, 20 insertions(+), 12 deletions(-)

diffs (74 lines):

diff -r 8282ce8b184f -r f2a523effa0b sys/kern/kern_lwp.c
--- a/sys/kern/kern_lwp.c       Tue Dec 21 18:59:22 2021 +0000
+++ b/sys/kern/kern_lwp.c       Tue Dec 21 19:00:37 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: kern_lwp.c,v 1.244 2021/09/28 15:05:42 thorpej Exp $   */
+/*     $NetBSD: kern_lwp.c,v 1.245 2021/12/21 19:00:37 thorpej Exp $   */
 
 /*-
  * Copyright (c) 2001, 2006, 2007, 2008, 2009, 2019, 2020
@@ -217,7 +217,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_lwp.c,v 1.244 2021/09/28 15:05:42 thorpej Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_lwp.c,v 1.245 2021/12/21 19:00:37 thorpej Exp $");
 
 #include "opt_ddb.h"
 #include "opt_lockdebug.h"
@@ -262,6 +262,7 @@
 
 static int             lwp_ctor(void *, void *, int);
 static void            lwp_dtor(void *, void *);
+static void            lwp_pre_dtor(void *);
 
 /* DTrace proc provider probes */
 SDT_PROVIDER_DEFINE(proc);
@@ -341,6 +342,7 @@
        lwpinit_specificdata();
        lwp_cache = pool_cache_init(sizeof(lwp_t), MIN_LWP_ALIGNMENT, 0, 0,
            "lwppl", NULL, IPL_NONE, lwp_ctor, lwp_dtor, NULL);
+       pool_cache_setpredestruct(lwp_cache, lwp_pre_dtor);
 
        maxlwp = cpu_maxlwp();
        sysctl_kern_lwp_setup();
@@ -391,23 +393,29 @@
 }
 
 static void
+lwp_pre_dtor(void *arg __unused)
+{
+       /*
+        * Provide a barrier to ensure that all mutex_oncpu() and rw_oncpu()
+        * calls will exit before memory of LWPs is returned to the pool, where
+        * KVA of LWP structure might be freed and re-used for other purposes.
+        * Kernel preemption is disabled around mutex_oncpu() and rw_oncpu()
+        * callers, therefore cross-call to all CPUs will do the job.
+        *
+        * XXX should use epoch based reclamation.
+        */
+       xc_barrier(0);
+}
+
+static void
 lwp_dtor(void *arg, void *obj)
 {
        lwp_t *l = obj;
-       (void)l;
 
        /*
-        * Provide a barrier to ensure that all mutex_oncpu() and rw_oncpu()
-        * calls will exit before memory of LWP is returned to the pool, where
-        * KVA of LWP structure might be freed and re-used for other purposes.
-        * Kernel preemption is disabled around mutex_oncpu() and rw_oncpu()
-        * callers, therefore cross-call to all CPUs will do the job.  Also,
-        * the value of l->l_cpu must be still valid at this point.
-        *
-        * XXX should use epoch based reclamation.
+        * The value of l->l_cpu must still be valid at this point.
         */
        KASSERT(l->l_cpu != NULL);
-       xc_barrier(0);
 
        /*
         * We can't return turnstile0 to the pool (it didn't come from it),