linux-kernel - Re: [RFC PATCH v2 2/3] wifi: cfg80211: add a workqueue with special semantics

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Message-ID: <aa7a0e08edf6567db027058cd331dfae86f54e62.camel@sipsolutions.net>
Date:   Thu, 11 May 2023 23:50:35 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     linux-kernel@...r.kernel.org
Cc:     linux-wireless@...r.kernel.org, Tejun Heo <tj@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [RFC PATCH v2 2/3] wifi: cfg80211: add a workqueue with special
 semantics

Now that I look at this more ...

> +static void cfg80211_wiphy_work(struct work_struct *work)
> +{
> +	struct cfg80211_registered_device *rdev;
> +
> +	rdev = container_of(work, struct cfg80211_registered_device, wiphy_work);
> +
> +	spin_lock_irq(&rdev->wiphy_work_lock);
> +	while (!list_empty(&rdev->wiphy_work_list)) {
> +		struct wiphy_work *wk;
> +
> +		wk = list_first_entry(&rdev->wiphy_work_list,
> +				      struct wiphy_work, entry);
> +		list_del_init(&wk->entry);
> +		spin_unlock_irq(&rdev->wiphy_work_lock);
> +
> +		mutex_lock(&rdev->wiphy.mtx);

If I just change the locking here to take the wiphy.mtx before looking
at the list, which basically doesn't matter, then I don't even need
workqueue_pause() and all, nor do I even need a separate workqueue, just
schedule_work() will be good enough ... Just needs a _bit_ more work
when cancelling and here we should reschedule the work if the list isn't
empty after the first round, but overall that ends up far simpler.

So I think I'll drop the workqueue pause/resume the next time around,
FWIW.

johannes