[src/trunk]: src/sys/external/bsd/drm2/linux linux: In kthread_park, wake thr...

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

details:   https://anonhg.NetBSD.org/src/rev/176904b3198e
branches:  trunk
changeset: 1028986:176904b3198e
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Sun Dec 19 12:38:56 2021 +0000

description:
linux: In kthread_park, wake thread to re-check kthread_shouldpark.

Otherwise, the thread to pakr may be sleeping on some condvar not
noticing it has to notify kthread_park --> deadlock.

diffstat:

 sys/external/bsd/drm2/linux/linux_kthread.c |  39 ++++++++++++++++++++++++++--
 1 files changed, 36 insertions(+), 3 deletions(-)

diffs (66 lines):

diff -r f3c5ed506fc9 -r 176904b3198e sys/external/bsd/drm2/linux/linux_kthread.c
--- a/sys/external/bsd/drm2/linux/linux_kthread.c       Sun Dec 19 12:38:49 2021 +0000
+++ b/sys/external/bsd/drm2/linux/linux_kthread.c       Sun Dec 19 12:38:56 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: linux_kthread.c,v 1.3 2021/12/19 12:29:39 riastradh Exp $      */
+/*     $NetBSD: linux_kthread.c,v 1.4 2021/12/19 12:38:56 riastradh Exp $      */
 
 /*-
  * Copyright (c) 2021 The NetBSD Foundation, Inc.
@@ -30,7 +30,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: linux_kthread.c,v 1.3 2021/12/19 12:29:39 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: linux_kthread.c,v 1.4 2021/12/19 12:38:56 riastradh Exp $");
 
 #include <sys/types.h>
 
@@ -184,13 +184,46 @@
 void
 kthread_park(struct task_struct *T)
 {
+       struct lwp *l;
 
        mutex_enter(&T->kt_lock);
+
+       /* Caller must not ask to park if they've already asked to stop.  */
        KASSERT(!T->kt_shouldstop);
+
+       /* Ask the thread to park.  */
        T->kt_shouldpark = true;
+
+       /* Don't wait for ourselves -- Linux allows this semantics.  */
+       if ((l = T->kt_lwp) == curlwp)
+               goto out;
+
+       /*
+        * If the thread is asleep for any reason, give it a spurious
+        * wakeup.  The thread is responsible for checking
+        * kthread_shouldpark before sleeping.  This logic is like
+        * sleepq_timeout, but without setting LW_STIMO.
+        */
+       lwp_lock(l);
+       if (l->l_wchan == NULL) {
+               /*
+                * Not sleeping, so no need to wake up -- the thread
+                * will eventually check kthread_shouldpark.
+                */
+               lwp_unlock(l);
+       } else {
+               /*
+                * Sleeping, so wake it up.  lwp_unsleep has the side
+                * effect of unlocking l when we pass unlock=true.
+                */
+               lwp_unsleep(l, /*unlock*/true);
+       }
+
+       /* Wait until the thread has issued kthread_parkme.  */
        while (!T->kt_parked)
                cv_wait(&T->kt_cv, &T->kt_lock);
-       mutex_exit(&T->kt_lock);
+
+out:   mutex_exit(&T->kt_lock);
 }
 
 void