netdev - Re: [PATCH] wwan_hwsim: Avoid flush_scheduled

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Date:   Wed, 20 Apr 2022 19:17:53 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Loic Poulain <loic.poulain@...aro.org>
Cc:     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>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH] wwan_hwsim: Avoid flush_scheduled_work() usage

On 2022/04/20 18:53, Loic Poulain wrote:
>> @@ -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:

Do you want

	debugfs_remove(wwan_hwsim_debugfs_devcreate);

here (as a separate patch)?

>>         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 */
> 
> Wouldn't it be simpler to just remove the flush call. It Looks like
> all ports have been removed at that point, and all works cancelled,
> right?

I guess that this flush_scheduled_work() is for waiting for schedule_work(&dev->del_work) from
wwan_hwsim_debugfs_devdestroy_write(). That is, if wwan_hwsim_debugfs_devdestroy_write() already
scheduled this work, wwan_hwsim_dev_del() from wwan_hwsim_dev_del_work() might be still in progress
even after wwan_hwsim_dev_del() from wwan_hwsim_free_devs() from wwan_hwsim_exit() returned.