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

From: Johannes Berg
Date: Wed May 10 2023 - 16:12:23 EST

From: Johannes Berg <johannes.berg@xxxxxxxxx>

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@xxxxxxxxx>
---
v2:
- dropped the previous workqueue locking patch
- therefore, rework this to have a specific wiphy
work struct (and delayed), which is maybe better
anyway since it's (more) type-safe
---
include/net/cfg80211.h | 109 +++++++++++++++++++++++++++-----
net/wireless/core.c | 138 +++++++++++++++++++++++++++++++++++++++++
net/wireless/core.h | 6 ++
net/wireless/nl80211.c | 8 ++-
4 files changed, 245 insertions(+), 16 deletions(-)

diff --git a/include/net/cfg80211.h b/include/net/cfg80211.h
index f115b2550309..c9318ddf495e 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 */

@@ -5669,31 +5673,108 @@ 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);
+
+struct wiphy_work;
+typedef void (*wiphy_work_func_t)(struct wiphy *, struct wiphy_work *);
+
+struct wiphy_work {
+ struct list_head entry;
+ wiphy_work_func_t func;
+};
+
+static inline void wiphy_work_init(struct wiphy_work *work,
+ wiphy_work_func_t func)
{
- __release(&wiphy->mtx);
- mutex_unlock(&wiphy->mtx);
+ INIT_LIST_HEAD(&work->entry);
+ work->func = func;
}

+/**
+ * wiphy_work_queue - queue work for the wiphy
+ * @wiphy: the wiphy to queue for
+ * @work: the work item
+ *
+ * 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_work_queue(struct wiphy *wiphy, struct wiphy_work *work);
+
+/**
+ * wiphy_work_cancel - 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().
+ */
+void wiphy_work_cancel(struct wiphy *wiphy, struct wiphy_work *work);
+
+struct wiphy_delayed_work {
+ struct wiphy_work work;
+ struct wiphy *wiphy;
+ struct timer_list timer;
+};
+
+void wiphy_delayed_work_timer(struct timer_list *t);
+
+static inline void wiphy_delayed_work_init(struct wiphy_delayed_work *dwork,
+ wiphy_work_func_t func)
+{
+ timer_setup(&dwork->timer, wiphy_delayed_work_timer, 0);
+ wiphy_work_init(&dwork->work, func);
+}
+
+/**
+ * wiphy_delayed_work_queue - 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_delayed_work_queue(struct wiphy *wiphy,
+ struct wiphy_delayed_work *dwork,
+ unsigned long delay);
+
+/**
+ * wiphy_delayed_work_cancel - 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().
+ */
+void wiphy_delayed_work_cancel(struct wiphy *wiphy,
+ struct wiphy_delayed_work *dwork);
+
/**
* struct wireless_dev - wireless device state
*
diff --git a/net/wireless/core.c b/net/wireless/core.c
index 5b0c4d5b80cf..357fd5425bff 100644
--- a/net/wireless/core.c
+++ b/net/wireless/core.c
@@ -408,6 +408,28 @@ static void cfg80211_propagate_cac_done_wk(struct work_struct *work)
rtnl_unlock();
}

+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);
+ wk->func(&rdev->wiphy, wk);
+ mutex_unlock(&rdev->wiphy.mtx);
+ }
+ spin_unlock_irq(&rdev->wiphy_work_lock);
+}
+
/* exported functions */

struct wiphy *wiphy_new_nm(const struct cfg80211_ops *ops, int sizeof_priv,
@@ -533,6 +555,15 @@ struct wiphy *wiphy_new_nm(const struct cfg80211_ops *ops, int sizeof_priv,
return NULL;
}

+ rdev->wq = alloc_workqueue("%s", 0, 0, dev_name(&rdev->wiphy.dev));
+ if (!rdev->wq) {
+ wiphy_free(&rdev->wiphy);
+ return NULL;
+ }
+
+ INIT_WORK(&rdev->wiphy_work, cfg80211_wiphy_work);
+ INIT_LIST_HEAD(&rdev->wiphy_work_list);
+ spin_lock_init(&rdev->wiphy_work_lock);
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 +1099,13 @@ 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 +1131,10 @@ 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 +1606,102 @@ 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_work_queue(struct wiphy *wiphy, struct wiphy_work *work)
+{
+ struct cfg80211_registered_device *rdev = wiphy_to_rdev(wiphy);
+ unsigned long flags;
+
+ spin_lock_irqsave(&rdev->wiphy_work_lock, flags);
+ if (list_empty(&work->entry))
+ list_add_tail(&rdev->wiphy_work_list, &work->entry);
+ spin_unlock_irqrestore(&rdev->wiphy_work_lock, flags);
+
+ queue_work(rdev->wq, &rdev->wiphy_work);
+}
+EXPORT_SYMBOL_GPL(wiphy_work_queue);
+
+void wiphy_work_cancel(struct wiphy *wiphy, struct wiphy_work *work)
+{
+ struct cfg80211_registered_device *rdev = wiphy_to_rdev(wiphy);
+ unsigned long flags;
+
+#ifdef CONFIG_LOCKDEP
+ lockdep_assert_held(&wiphy->mtx);
+ WARN_ON_ONCE(!wiphy->mtx_fully_held);
+#endif
+ spin_lock_irqsave(&rdev->wiphy_work_lock, flags);
+ if (!list_empty(&work->entry))
+ list_del_init(&work->entry);
+ spin_unlock_irqrestore(&rdev->wiphy_work_lock, flags);
+}
+EXPORT_SYMBOL_GPL(wiphy_work_cancel);
+
+void wiphy_delayed_work_timer(struct timer_list *t)
+{
+ struct wiphy_delayed_work *dwork = from_timer(dwork, t, timer);
+
+ wiphy_work_queue(dwork->wiphy, &dwork->work);
+}
+EXPORT_SYMBOL(wiphy_delayed_work_timer);
+
+void wiphy_delayed_work_queue(struct wiphy *wiphy,
+ struct wiphy_delayed_work *dwork,
+ unsigned long delay)
+{
+ if (!delay) {
+ wiphy_work_queue(wiphy, &dwork->work);
+ return;
+ }
+
+ dwork->wiphy = wiphy;
+ mod_timer(&dwork->timer, jiffies + delay);
+}
+EXPORT_SYMBOL_GPL(wiphy_delayed_work_queue);
+
+void wiphy_delayed_work_cancel(struct wiphy *wiphy,
+ struct wiphy_delayed_work *dwork)
+{
+#ifdef CONFIG_LOCKDEP
+ lockdep_assert_held(&wiphy->mtx);
+ WARN_ON_ONCE(!wiphy->mtx_fully_held);
+#endif
+ del_timer_sync(&dwork->timer);
+ wiphy_work_cancel(wiphy, &dwork->work);
+}
+EXPORT_SYMBOL_GPL(wiphy_delayed_work_cancel);
+
static int __init cfg80211_init(void)
{
int err;
diff --git a/net/wireless/core.h b/net/wireless/core.h
index 7c61752f6d83..adb45fa38acb 100644
--- a/net/wireless/core.h
+++ b/net/wireless/core.h
@@ -108,6 +108,12 @@ struct cfg80211_registered_device {
/* lock for all wdev lists */
spinlock_t mgmt_registrations_lock;

+ struct workqueue_struct *wq;
+ struct work_struct wiphy_work;
+ struct list_head wiphy_work_list;
+ /* protects the list above */
+ spinlock_t wiphy_work_lock;
+
/* 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