From: jsg <jsg@openbsd.org>
Date: Sat, 7 Aug 2021 06:23:34 +0000 (+0000)
Subject: use taskq_del_barrier() instead of taskq_barrier() when flushing work
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=2bb569e6635011dfd3c529013e7697994a48b787;p=openbsd

use taskq_del_barrier() instead of taskq_barrier() when flushing work

prompted by jcs@ reporting a protection fault trap in
drm_mode_rmfb_work_fn() while playing a youtube video in firefox on a
kaby lake machine.  He later saw the same trace on tiger lake.

The arguments to drm_mode_rmfb_work_fn() are on the stack in
drm_mode_rmfb() with flush_work() called before return.

taskq_barrier() is only a barrier for running not queued tasks.

I suspect the linux functions expect any previously queued work to
complete not just any currently running work.  I'm not sure if the
difference matters in practice.
---

diff --git a/sys/dev/pci/drm/drm_linux.c b/sys/dev/pci/drm/drm_linux.c
index 72c53210f6f..5cc7459a583 100644
--- a/sys/dev/pci/drm/drm_linux.c
+++ b/sys/dev/pci/drm/drm_linux.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: drm_linux.c,v 1.82 2021/07/28 13:28:04 kettenis Exp $	*/
+/*	$OpenBSD: drm_linux.c,v 1.83 2021/08/07 06:23:34 jsg Exp $	*/
 /*
  * Copyright (c) 2013 Jonathan Gray <jsg@openbsd.org>
  * Copyright (c) 2015, 2016 Mark Kettenis <kettenis@openbsd.org>
@@ -171,7 +171,7 @@ flush_work(struct work_struct *work)
 		return false;
 
 	if (work->tq)
-		taskq_barrier(work->tq);
+		taskq_del_barrier(work->tq, &work->task);
 	return false;
 }
 
@@ -189,7 +189,7 @@ flush_delayed_work(struct delayed_work *dwork)
 	}
 
 	if (dwork->tq)
-		taskq_barrier(dwork->tq);
+		taskq_del_barrier(dwork->tq, &dwork->work.task);
 	return ret;
 }
 
@@ -288,7 +288,7 @@ kthread_flush_work(struct kthread_work *work)
 		return;
 
 	if (work->tq)
-		taskq_barrier(work->tq);
+		taskq_del_barrier(work->tq, &work->task);
 }
 
 void
diff --git a/sys/dev/pci/drm/include/linux/irq_work.h b/sys/dev/pci/drm/include/linux/irq_work.h
index f9df2099cd9..30daa6f6b39 100644
--- a/sys/dev/pci/drm/include/linux/irq_work.h
+++ b/sys/dev/pci/drm/include/linux/irq_work.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: irq_work.h,v 1.3 2021/07/07 02:38:36 jsg Exp $	*/
+/*	$OpenBSD: irq_work.h,v 1.4 2021/08/07 06:23:34 jsg Exp $	*/
 /*
  * Copyright (c) 2015 Mark Kettenis
  *
@@ -49,7 +49,7 @@ irq_work_queue(struct irq_work *work)
 static inline void
 irq_work_sync(struct irq_work *work)
 {
-	taskq_barrier(work->tq);
+	taskq_del_barrier(work->tq, &work->task);
 }
 
 #endif