Message-Id: <20230510175846.831b26b9978f.I28a06f59bf647db6dea519e6fca1894f94227d73@changeid>
Date:   Wed, 10 May 2023 18:04:27 +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>,
        Johannes Berg <johannes.berg@...el.com>
Subject: [RFC PATCH 3/4] wifi: cfg80211: add a workqueue with special semantics

From: Johannes Berg <johannes.berg@...el.com>

The special semantics are that it's paused during wiphy_lock()
and nothing can run or even start running on it while that is
locked.

Signed-off-by: Johannes Berg <johannes.berg@...el.com>
---
 include/net/cfg80211.h | 93 +++++++++++++++++++++++++++++++++++-------
 net/wireless/core.c    | 68 ++++++++++++++++++++++++++++++
 net/wireless/core.h    |  2 +
 net/wireless/nl80211.c |  8 +++-
 4 files changed, 155 insertions(+), 16 deletions(-)

diff --git a/include/net/cfg80211.h b/include/net/cfg80211.h
index f115b2550309..f30ecbac7490 100644
--- a/include/net/cfg80211.h
+++ b/include/net/cfg80211.h
@@ -5142,6 +5142,7 @@ struct wiphy_iftype_akm_suites {
 /**
  * struct wiphy - wireless hardware description
  * @mtx: mutex for the data (structures) of this device
+ * @mtx_fully_held: the mutex was held with workqueue pause/flush
  * @reg_notifier: the driver's regulatory notification callback,
  *	note that if your driver uses wiphy_apply_custom_regulatory()
  *	the reg_notifier's request can be passed as NULL
@@ -5351,6 +5352,9 @@ struct wiphy_iftype_akm_suites {
  */
 struct wiphy {
 	struct mutex mtx;
+#ifdef CONFIG_LOCKDEP
+	bool mtx_fully_held;
+#endif
 
 	/* assign these fields before you register the wiphy */
 
@@ -5669,29 +5673,90 @@ struct cfg80211_cqm_config;
  * wiphy_lock - lock the wiphy
  * @wiphy: the wiphy to lock
  *
- * This is mostly exposed so it can be done around registering and
- * unregistering netdevs that aren't created through cfg80211 calls,
- * since that requires locking in cfg80211 when the notifiers is
- * called, but that cannot differentiate which way it's called.
+ * This is needed around registering and unregistering netdevs that
+ * aren't created through cfg80211 calls, since that requires locking
+ * in cfg80211 when the notifiers is called, but that cannot
+ * differentiate which way it's called.
+ *
+ * It can also be used by drivers for their own purposes.
  *
  * When cfg80211 ops are called, the wiphy is already locked.
+ *
+ * Note that this makes sure that no workers that have been queued
+ * with wiphy_queue_work() are running.
  */
-static inline void wiphy_lock(struct wiphy *wiphy)
-	__acquires(&wiphy->mtx)
-{
-	mutex_lock(&wiphy->mtx);
-	__acquire(&wiphy->mtx);
-}
+void wiphy_lock(struct wiphy *wiphy) __acquires(&wiphy->mtx);
 
 /**
  * wiphy_unlock - unlock the wiphy again
  * @wiphy: the wiphy to unlock
  */
-static inline void wiphy_unlock(struct wiphy *wiphy)
-	__releases(&wiphy->mtx)
+void wiphy_unlock(struct wiphy *wiphy) __releases(&wiphy->mtx);
+
+/**
+ * wiphy_queue_work - queue work for the wiphy
+ * @wiphy: the wiphy to queue for
+ * @work: the worker
+ *
+ * This is useful for work that must be done asynchronously, and work
+ * queued here has the special property that the wiphy mutex will be
+ * held as if wiphy_lock() was called, and that it cannot be running
+ * after wiphy_lock() was called. Therefore, wiphy_cancel_work() can
+ * use just cancel_work() instead of cancel_work_sync(), it requires
+ * being in a section protected by wiphy_lock().
+ */
+void wiphy_queue_work(struct wiphy *wiphy, struct work_struct *work);
+
+/**
+ * wiphy_cancel_work - cancel previously queued work
+ * @wiphy: the wiphy, for debug purposes
+ * @work: the work to cancel
+ *
+ * Cancel the work *without* waiting for it, this assumes being
+ * called under the wiphy mutex acquired by wiphy_lock().
+ */
+static inline void wiphy_cancel_work(struct wiphy *wiphy, struct work_struct *work)
 {
-	__release(&wiphy->mtx);
-	mutex_unlock(&wiphy->mtx);
+#ifdef CONFIG_LOCKDEP
+	lockdep_assert_held(&wiphy->mtx);
+	WARN_ON_ONCE(!wiphy->mtx_fully_held);
+#endif
+	cancel_work(work);
+}
+
+/**
+ * wiphy_queue_delayed_work - queue delayed work for the wiphy
+ * @wiphy: the wiphy to queue for
+ * @dwork: the delayable worker
+ * @delay: number of jiffies to wait before queueing
+ *
+ * This is useful for work that must be done asynchronously, and work
+ * queued here has the special property that the wiphy mutex will be
+ * held as if wiphy_lock() was called, and that it cannot be running
+ * after wiphy_lock() was called. Therefore, wiphy_cancel_work() can
+ * use just cancel_work() instead of cancel_work_sync(), it requires
+ * being in a section protected by wiphy_lock().
+ */
+void wiphy_queue_delayed_work(struct wiphy *wiphy,
+			      struct delayed_work *dwork,
+			      unsigned long delay);
+
+/**
+ * wiphy_cancel_delayed_work - cancel previously queued delayed work
+ * @wiphy: the wiphy, for debug purposes
+ * @dwork: the delayed work to cancel
+ *
+ * Cancel the work *without* waiting for it, this assumes being
+ * called under the wiphy mutex acquired by wiphy_lock().
+ */
+static inline void wiphy_cancel_delayed_work(struct wiphy *wiphy,
+					     struct delayed_work *dwork)
+{
+#ifdef CONFIG_LOCKDEP
+	lockdep_assert_held(&wiphy->mtx);
+	WARN_ON_ONCE(!wiphy->mtx_fully_held);
+#endif
+	cancel_delayed_work(dwork);
 }
 
 /**
diff --git a/net/wireless/core.c b/net/wireless/core.c
index 5b0c4d5b80cf..11e600c71fb6 100644
--- a/net/wireless/core.c
+++ b/net/wireless/core.c
@@ -533,6 +533,13 @@ struct wiphy *wiphy_new_nm(const struct cfg80211_ops *ops, int sizeof_priv,
 		return NULL;
 	}
 
+	rdev->wq = alloc_ordered_workqueue_mtx("%s", 0, &rdev->wiphy.mtx,
+					       dev_name(&rdev->wiphy.dev));
+	if (!rdev->wq) {
+		wiphy_free(&rdev->wiphy);
+		return NULL;
+	}
+
 	INIT_WORK(&rdev->rfkill_block, cfg80211_rfkill_block_work);
 	INIT_WORK(&rdev->conn_work, cfg80211_conn_work);
 	INIT_WORK(&rdev->event_work, cfg80211_event_work);
@@ -1068,6 +1075,13 @@ void wiphy_unregister(struct wiphy *wiphy)
 	wiphy_unlock(&rdev->wiphy);
 	rtnl_unlock();
 
+	/*
+	 * flush again, even if wiphy_lock() did above, something might
+	 * have been reaching it still while the code above was running,
+	 * e.g. via debugfs.
+	 */
+	flush_workqueue(rdev->wq);
+
 	flush_work(&rdev->scan_done_wk);
 	cancel_work_sync(&rdev->conn_work);
 	flush_work(&rdev->event_work);
@@ -1093,6 +1107,10 @@ void cfg80211_dev_free(struct cfg80211_registered_device *rdev)
 {
 	struct cfg80211_internal_bss *scan, *tmp;
 	struct cfg80211_beacon_registration *reg, *treg;
+
+	if (rdev->wq) /* might be NULL in error cases */
+		destroy_workqueue(rdev->wq);
+
 	rfkill_destroy(rdev->wiphy.rfkill);
 	list_for_each_entry_safe(reg, treg, &rdev->beacon_registrations, list) {
 		list_del(&reg->list);
@@ -1564,6 +1582,56 @@ static struct pernet_operations cfg80211_pernet_ops = {
 	.exit = cfg80211_pernet_exit,
 };
 
+void wiphy_lock(struct wiphy *wiphy)
+{
+	struct cfg80211_registered_device *rdev = wiphy_to_rdev(wiphy);
+
+	workqueue_pause(rdev->wq);
+
+	mutex_lock(&wiphy->mtx);
+
+#ifdef CONFIG_LOCKDEP
+	wiphy->mtx_fully_held = true;
+#endif
+}
+EXPORT_SYMBOL(wiphy_lock);
+
+void wiphy_unlock(struct wiphy *wiphy)
+{
+	struct cfg80211_registered_device *rdev = wiphy_to_rdev(wiphy);
+
+#ifdef CONFIG_LOCKDEP
+	WARN_ON_ONCE(!wiphy->mtx_fully_held);
+#endif
+
+	workqueue_resume(rdev->wq);
+
+#ifdef CONFIG_LOCKDEP
+	wiphy->mtx_fully_held = false;
+#endif
+
+	mutex_unlock(&wiphy->mtx);
+}
+EXPORT_SYMBOL(wiphy_unlock);
+
+void wiphy_queue_work(struct wiphy *wiphy, struct work_struct *work)
+{
+	struct cfg80211_registered_device *rdev = wiphy_to_rdev(wiphy);
+
+	queue_work(rdev->wq, work);
+}
+EXPORT_SYMBOL(wiphy_queue_work);
+
+void wiphy_queue_delayed_work(struct wiphy *wiphy,
+			      struct delayed_work *dwork,
+			      unsigned long delay)
+{
+	struct cfg80211_registered_device *rdev = wiphy_to_rdev(wiphy);
+
+	queue_delayed_work(rdev->wq, dwork, delay);
+}
+EXPORT_SYMBOL(wiphy_queue_delayed_work);
+
 static int __init cfg80211_init(void)
 {
 	int err;
diff --git a/net/wireless/core.h b/net/wireless/core.h
index 7c61752f6d83..0ab79cc28adb 100644
--- a/net/wireless/core.h
+++ b/net/wireless/core.h
@@ -108,6 +108,8 @@ struct cfg80211_registered_device {
 	/* lock for all wdev lists */
 	spinlock_t mgmt_registrations_lock;
 
+	struct workqueue_struct *wq;
+
 	/* must be last because of the way we do wiphy_priv(),
 	 * and it should at least be aligned to NETDEV_ALIGN */
 	struct wiphy wiphy __aligned(NETDEV_ALIGN);
diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index 112b4bb009c8..1fb4978f7649 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -1002,7 +1002,9 @@ static int nl80211_prepare_wdev_dump(struct netlink_callback *cb,
 			return PTR_ERR(*wdev);
 		}
 		*rdev = wiphy_to_rdev((*wdev)->wiphy);
-		mutex_lock(&(*rdev)->wiphy.mtx);
+		wiphy_lock(&(*rdev)->wiphy);
+		/* the conditional locking is too hard for sparse */
+		__release(&(*rdev)->wiphy.mtx);
 		rtnl_unlock();
 		/* 0 is the first index - add 1 to parse only once */
 		cb->args[0] = (*rdev)->wiphy_idx + 1;
@@ -1032,7 +1034,9 @@ static int nl80211_prepare_wdev_dump(struct netlink_callback *cb,
 			rtnl_unlock();
 			return -ENODEV;
 		}
-		mutex_lock(&(*rdev)->wiphy.mtx);
+		wiphy_lock(&(*rdev)->wiphy);
+		/* the conditional locking is too hard for sparse */
+		__release(&(*rdev)->wiphy.mtx);
 		rtnl_unlock();
 	}
 
-- 
2.40.1

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