Sun Dec 19 12:38:56 2021 UTC ()

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.


(riastradh)

diff -r1.3 -r1.4 src/sys/external/bsd/drm2/linux/linux_kthread.c

--- src/sys/external/bsd/drm2/linux/linux_kthread.c 2021/12/19 12:29:39	1.3
+++ src/sys/external/bsd/drm2/linux/linux_kthread.c 2021/12/19 12:38:56	1.4

 @@ -1,14 +1,14 @@
-/*	$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.
  * All rights reserved.
+ *
  * This code is derived from software contributed to The NetBSD Foundation
  * by Taylor R. Campbell.
+ *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
 @@ -20,27 +20,27 @@
  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  * POSSIBILITY OF SUCH DAMAGE.
  */
 #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>
 #include <sys/condvar.h>
 #include <sys/kmem.h>
 #include <sys/kthread.h>
 #include <sys/lwp.h>
 #include <sys/mutex.h>
 #include <sys/specificdata.h>
 #include <linux/kthread.h>
 struct task_struct {
 @@ -174,33 +174,66 @@ kthread_should_stop(void)
 	struct task_struct *T = linux_kthread();
 	bool shouldstop;
 	mutex_enter(&T->kt_lock);
 	shouldstop = T->kt_shouldstop;
 	mutex_exit(&T->kt_lock);
 	return shouldstop;
+}
 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
 kthread_unpark(struct task_struct *T)
+{
 	mutex_enter(&T->kt_lock);
 	T->kt_shouldpark = false;
 	cv_broadcast(&T->kt_cv);
 	mutex_exit(&T->kt_lock);
+}
 int