[src/trunk]: src/sys/kern Restore curlwp->l_name in threadpool_job_done(), ra...

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

details:   https://anonhg.NetBSD.org/src/rev/1c12a59ba74d
branches:  trunk
changeset: 837918:1c12a59ba74d
user:      thorpej <thorpej%NetBSD.org@localhost>
date:      Thu Dec 27 04:45:29 2018 +0000

description:
Restore curlwp->l_name in threadpool_job_done(), rather than after the
job function has returned.  This lays the groundwork for some job object
reference counting change that will be coming in a subsequent comment.

diffstat:

 sys/kern/kern_threadpool.c |  35 +++++++++++++++++++++++------------
 1 files changed, 23 insertions(+), 12 deletions(-)

diffs (78 lines):

diff -r a56df05fe3f4 -r 1c12a59ba74d sys/kern/kern_threadpool.c
--- a/sys/kern/kern_threadpool.c        Thu Dec 27 02:54:00 2018 +0000
+++ b/sys/kern/kern_threadpool.c        Thu Dec 27 04:45:29 2018 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: kern_threadpool.c,v 1.11 2018/12/26 22:16:26 thorpej Exp $     */
+/*     $NetBSD: kern_threadpool.c,v 1.12 2018/12/27 04:45:29 thorpej 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 1.11 2018/12/26 22:16:26 thorpej Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_threadpool.c,v 1.12 2018/12/27 04:45:29 thorpej Exp $");
 
 #include <sys/types.h>
 #include <sys/param.h>
@@ -107,6 +107,7 @@
 
 struct threadpool_thread {
        struct lwp                      *tpt_lwp;
+       char                            *tpt_lwp_savedname;
        struct threadpool               *tpt_pool;
        struct threadpool_job           *tpt_job;
        kcondvar_t                      tpt_cv;
@@ -693,6 +694,15 @@
        KASSERT(job->job_thread != NULL);
        KASSERT(job->job_thread->tpt_lwp == curlwp);
 
+       /*
+        * We can safely read this field; it's only modified right before
+        * we call the job work function, and we are only preserving it
+        * to use here; no one cares if it contains junk afterward.
+        */
+       lwp_lock(curlwp);
+       curlwp->l_name = job->job_thread->tpt_lwp_savedname;
+       lwp_unlock(curlwp);
+
        cv_broadcast(&job->job_cv);
        job->job_thread = NULL;
 }
@@ -977,24 +987,25 @@
 
                struct threadpool_job *const job = thread->tpt_job;
                KASSERT(job != NULL);
+
+               /* Set our lwp name to reflect what job we're doing.  */
+               lwp_lock(curlwp);
+               char *const lwp_name __diagused = curlwp->l_name;
+               thread->tpt_lwp_savedname = curlwp->l_name;
+               curlwp->l_name = job->job_name;
+               lwp_unlock(curlwp);
+
                mutex_spin_exit(&pool->tp_lock);
 
                TP_LOG(("%s: running job '%s' on thread %p.\n",
                    __func__, job->job_name, thread));
 
-               /* Set our lwp name to reflect what job we're doing.  */
-               lwp_lock(curlwp);
-               char *const lwp_name = curlwp->l_name;
-               curlwp->l_name = job->job_name;
-               lwp_unlock(curlwp);
-
                /* Run the job.  */
                (*job->job_fn)(job);
 
-               /* Restore our lwp name.  */
-               lwp_lock(curlwp);
-               curlwp->l_name = lwp_name;
-               lwp_unlock(curlwp);
+               /* lwp name restored in threadpool_job_done(). */
+               KASSERTMSG((curlwp->l_name == lwp_name),
+                   "someone forgot to call threadpool_job_done()!");
 
                /* Job is done and its name is unreferenced.  Release it.  */
                threadpool_job_rele(job);