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Date:   Wed, 20 Apr 2022 11:22:10 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Loic Poulain <loic.poulain@...aro.org>,
        Sergey Ryazanov <ryazanov.s.a@...il.com>,
        Johannes Berg <johannes@...solutions.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     Network Development <netdev@...r.kernel.org>
Subject: [PATCH] wwan_hwsim: Avoid flush_scheduled_work() usage

Flushing system-wide workqueues is dangerous and will be forbidden.
Replace system_wq with local wwan_wq.

Link: https://lkml.kernel.org/r/49925af7-78a8-a3dd-bce6-cfc02e1a9236@I-love.SAKURA.ne.jp
Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
---
Note: This patch is only compile tested. By the way, don't you want to call
debugfs_remove(wwan_hwsim_debugfs_devcreate) at err_clean_devs label in
wwan_hwsim_init() like wwan_hwsim_exit() does, for debugfs_create_file("devcreate")
is called before "goto err_clean_devs" happens?

 drivers/net/wwan/wwan_hwsim.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/net/wwan/wwan_hwsim.c b/drivers/net/wwan/wwan_hwsim.c
index 5b62cf3b3c42..2136319f588f 100644
--- a/drivers/net/wwan/wwan_hwsim.c
+++ b/drivers/net/wwan/wwan_hwsim.c
@@ -33,6 +33,7 @@ static struct dentry *wwan_hwsim_debugfs_devcreate;
 static DEFINE_SPINLOCK(wwan_hwsim_devs_lock);
 static LIST_HEAD(wwan_hwsim_devs);
 static unsigned int wwan_hwsim_dev_idx;
+static struct workqueue_struct *wwan_wq;
 
 struct wwan_hwsim_dev {
 	struct list_head list;
@@ -371,7 +372,7 @@ static ssize_t wwan_hwsim_debugfs_portdestroy_write(struct file *file,
 	 * waiting this callback to finish in the debugfs_remove() call. So,
 	 * use workqueue.
 	 */
-	schedule_work(&port->del_work);
+	queue_work(wwan_wq, &port->del_work);
 
 	return count;
 }
@@ -416,7 +417,7 @@ static ssize_t wwan_hwsim_debugfs_devdestroy_write(struct file *file,
 	 * waiting this callback to finish in the debugfs_remove() call. So,
 	 * use workqueue.
 	 */
-	schedule_work(&dev->del_work);
+	queue_work(wwan_wq, &dev->del_work);
 
 	return count;
 }
@@ -506,9 +507,15 @@ static int __init wwan_hwsim_init(void)
 	if (wwan_hwsim_devsnum < 0 || wwan_hwsim_devsnum > 128)
 		return -EINVAL;
 
+	wwan_wq = alloc_workqueue("wwan_wq", 0, 0);
+	if (!wwan_wq)
+		return -ENOMEM;
+
 	wwan_hwsim_class = class_create(THIS_MODULE, "wwan_hwsim");
-	if (IS_ERR(wwan_hwsim_class))
+	if (IS_ERR(wwan_hwsim_class)) {
+		destroy_workqueue(wwan_wq);
 		return PTR_ERR(wwan_hwsim_class);
+	}
 
 	wwan_hwsim_debugfs_topdir = debugfs_create_dir("wwan_hwsim", NULL);
 	wwan_hwsim_debugfs_devcreate =
@@ -524,6 +531,7 @@ static int __init wwan_hwsim_init(void)
 
 err_clean_devs:
 	wwan_hwsim_free_devs();
+	destroy_workqueue(wwan_wq);
 	debugfs_remove(wwan_hwsim_debugfs_topdir);
 	class_destroy(wwan_hwsim_class);
 
@@ -534,7 +542,7 @@ static void __exit wwan_hwsim_exit(void)
 {
 	debugfs_remove(wwan_hwsim_debugfs_devcreate);	/* Avoid new devs */
 	wwan_hwsim_free_devs();
-	flush_scheduled_work();		/* Wait deletion works completion */
+	destroy_workqueue(wwan_wq);		/* Wait deletion works completion */
 	debugfs_remove(wwan_hwsim_debugfs_topdir);
 	class_destroy(wwan_hwsim_class);
 }
-- 
2.32.0

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