[PATCH 0/2] cec core fixes

[PATCH 0/2] cec core fixes

[Hans Verkuil]

Two patches that fix two serious issues in the cec core framework.
The first will cause drivers that use the pin framework to stop
working in certain circumstances. Currently it affects only the
cec-gpio driver.

The second is a deadlock that can hit when closing the last open
filehandle of a driver that has an invalid physical address. Again,
this primarily hits cec-gpio, but I believe it can also happen
for other CEC drivers. This situation will typically occur when
monitoring the CEC traffic with cec-ctl --monitor and then stopping
cec-ctl with Ctrl-C.

While these patches should be backported, I decided to not to
send them out for 5.16 since I would like to give it more time for
testing.

Note also that a third issue was found with cec-pin where a atomic
operation can sleep. See:

https://lore.kernel.org/linux-media/a06e7c55-f25d-8339-faea-9be6d31d1c87@xs4all.nl/T/#u

The issue appears to be in the gpio and/or pinctrl framework.

Regards,

	Hans

Hans Verkuil (2):
  cec-pin: fix interrupt en/disable handling
  cec: fix a deadlock situation

 drivers/media/cec/core/cec-adap.c | 38 +++++++++++++++++--------------
 drivers/media/cec/core/cec-api.c  |  6 +++++
 drivers/media/cec/core/cec-core.c |  3 +++
 drivers/media/cec/core/cec-pin.c  | 31 ++++++++++++++-----------
 include/media/cec.h               | 11 +++++++--
 5 files changed, 57 insertions(+), 32 deletions(-)

-- 
2.33.0

[PATCH 1/2] cec-pin: fix interrupt en/disable handling

[Hans Verkuil]

The en/disable_irq() functions keep track of the 'depth': i.e. if
interrupts are disabled twice, then it needs to enable_irq() calls to
enable them again. The cec-pin framework didn't take this into accound
and could disable irqs multiple times, and it expected that a single
enable_irq() would enable them again.

Move all calls to en/disable_irq() to the kthread where it is easy
to keep track of the current irq state and ensure that multiple
en/disable_irq calls never happen.

If interrupts where disabled twice, then they would never turn on
again, leaving the CEC adapter in a dead state.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Fixes: 865463fc03ed (media: cec-pin: add error injection support)
Cc: <stable@vger.kernel.org>
---
 drivers/media/cec/core/cec-pin.c | 31 ++++++++++++++++++-------------
 1 file changed, 18 insertions(+), 13 deletions(-)

diff --git a/drivers/media/cec/core/cec-pin.c b/drivers/media/cec/core/cec-pin.c
index a60b6f03a6a1..178edc85dc92 100644
--- a/drivers/media/cec/core/cec-pin.c
+++ b/drivers/media/cec/core/cec-pin.c
@@ -1033,6 +1033,7 @@ static int cec_pin_thread_func(void *_adap)
 {
 	struct cec_adapter *adap = _adap;
 	struct cec_pin *pin = adap->pin;
+	bool irq_enabled = false;
 
 	for (;;) {
 		wait_event_interruptible(pin->kthread_waitq,
@@ -1060,6 +1061,7 @@ static int cec_pin_thread_func(void *_adap)
 				ns_to_ktime(pin->work_rx_msg.rx_ts));
 			msg->len = 0;
 		}
+
 		if (pin->work_tx_status) {
 			unsigned int tx_status = pin->work_tx_status;
 
@@ -1083,27 +1085,39 @@ static int cec_pin_thread_func(void *_adap)
 		switch (atomic_xchg(&pin->work_irq_change,
 				    CEC_PIN_IRQ_UNCHANGED)) {
 		case CEC_PIN_IRQ_DISABLE:
-			pin->ops->disable_irq(adap);
+			if (irq_enabled) {
+				pin->ops->disable_irq(adap);
+				irq_enabled = false;
+			}
 			cec_pin_high(pin);
 			cec_pin_to_idle(pin);
 			hrtimer_start(&pin->timer, ns_to_ktime(0),
 				      HRTIMER_MODE_REL);
 			break;
 		case CEC_PIN_IRQ_ENABLE:
+			if (irq_enabled)
+				break;
 			pin->enable_irq_failed = !pin->ops->enable_irq(adap);
 			if (pin->enable_irq_failed) {
 				cec_pin_to_idle(pin);
 				hrtimer_start(&pin->timer, ns_to_ktime(0),
 					      HRTIMER_MODE_REL);
+			} else {
+				irq_enabled = true;
 			}
 			break;
 		default:
 			break;
 		}
-
 		if (kthread_should_stop())
 			break;
 	}
+	if (pin->ops->disable_irq && irq_enabled)
+		pin->ops->disable_irq(adap);
+	hrtimer_cancel(&pin->timer);
+	cec_pin_read(pin);
+	cec_pin_to_idle(pin);
+	pin->state = CEC_ST_OFF;
 	return 0;
 }
 
@@ -1130,13 +1144,7 @@ static int cec_pin_adap_enable(struct cec_adapter *adap, bool enable)
 		hrtimer_start(&pin->timer, ns_to_ktime(0),
 			      HRTIMER_MODE_REL);
 	} else {
-		if (pin->ops->disable_irq)
-			pin->ops->disable_irq(adap);
-		hrtimer_cancel(&pin->timer);
 		kthread_stop(pin->kthread);
-		cec_pin_read(pin);
-		cec_pin_to_idle(pin);
-		pin->state = CEC_ST_OFF;
 	}
 	return 0;
 }
@@ -1157,11 +1165,8 @@ void cec_pin_start_timer(struct cec_pin *pin)
 	if (pin->state != CEC_ST_RX_IRQ)
 		return;
 
-	atomic_set(&pin->work_irq_change, CEC_PIN_IRQ_UNCHANGED);
-	pin->ops->disable_irq(pin->adap);
-	cec_pin_high(pin);
-	cec_pin_to_idle(pin);
-	hrtimer_start(&pin->timer, ns_to_ktime(0), HRTIMER_MODE_REL);
+	atomic_set(&pin->work_irq_change, CEC_PIN_IRQ_DISABLE);
+	wake_up_interruptible(&pin->kthread_waitq);
 }
 
 static int cec_pin_adap_transmit(struct cec_adapter *adap, u8 attempts,
-- 
2.33.0

[PATCH 2/2] cec: fix a deadlock situation

[Hans Verkuil]

The cec_devnode struct has a lock meant to serialize access
to the fields of this struct. This lock is taken during
device node (un)registration and when opening or releasing a
filehandle to the device node. When the last open filehandle
is closed the cec adapter might be disabled by calling the
adap_enable driver callback with the devnode.lock held.

However, if during that callback a message or event arrives
then the driver will call one of the cec_queue_event()
variants in cec-adap.c, and those will take the same devnode.lock
to walk the open filehandle list.

This obviously causes a deadlock.

This is quite easy to reproduce with the cec-gpio driver since that
uses the cec-pin framework which generated lots of events and uses
a kernel thread for the processing, so when adap_enable is called
the thread is still running and can generate events.

But I suspect that it might also happen with other drivers if an
interrupt arrives signaling e.g. a received message before adap_enable
had a chance to disable the interrupts.

This patch adds a new mutex to serialize access to the fhs list.
When adap_enable() is called the devnode.lock mutex is held, but
not devnode.lock_fhs. The event functions in cec-adap.c will now
use devnode.lock_fhs instead of devnode.lock, ensuring that it is
safe to call those functions from the adap_enable callback.

This specific issue only happens if the last open filehandle is closed
and the physical address is invalid. This is not something that
happens during normal operation, but it does happen when monitoring
CEC traffic (e.g. cec-ctl --monitor) with an unconfigured CEC adapter.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Cc: <stable@vger.kernel.org>  # for v5.13 and up
---
 drivers/media/cec/core/cec-adap.c | 38 +++++++++++++++++--------------
 drivers/media/cec/core/cec-api.c  |  6 +++++
 drivers/media/cec/core/cec-core.c |  3 +++
 include/media/cec.h               | 11 +++++++--
 4 files changed, 39 insertions(+), 19 deletions(-)

diff --git a/drivers/media/cec/core/cec-adap.c b/drivers/media/cec/core/cec-adap.c
index da73eb50cce2..857d6b1612c2 100644
--- a/drivers/media/cec/core/cec-adap.c
+++ b/drivers/media/cec/core/cec-adap.c
@@ -161,10 +161,10 @@ static void cec_queue_event(struct cec_adapter *adap,
 	u64 ts = ktime_get_ns();
 	struct cec_fh *fh;
 
-	mutex_lock(&adap->devnode.lock);
+	mutex_lock(&adap->devnode.lock_fhs);
 	list_for_each_entry(fh, &adap->devnode.fhs, list)
 		cec_queue_event_fh(fh, ev, ts);
-	mutex_unlock(&adap->devnode.lock);
+	mutex_unlock(&adap->devnode.lock_fhs);
 }
 
 /* Notify userspace that the CEC pin changed state at the given time. */
@@ -178,11 +178,12 @@ void cec_queue_pin_cec_event(struct cec_adapter *adap, bool is_high,
 	};
 	struct cec_fh *fh;
 
-	mutex_lock(&adap->devnode.lock);
-	list_for_each_entry(fh, &adap->devnode.fhs, list)
+	mutex_lock(&adap->devnode.lock_fhs);
+	list_for_each_entry(fh, &adap->devnode.fhs, list) {
 		if (fh->mode_follower == CEC_MODE_MONITOR_PIN)
 			cec_queue_event_fh(fh, &ev, ktime_to_ns(ts));
-	mutex_unlock(&adap->devnode.lock);
+	}
+	mutex_unlock(&adap->devnode.lock_fhs);
 }
 EXPORT_SYMBOL_GPL(cec_queue_pin_cec_event);
 
@@ -195,10 +196,10 @@ void cec_queue_pin_hpd_event(struct cec_adapter *adap, bool is_high, ktime_t ts)
 	};
 	struct cec_fh *fh;
 
-	mutex_lock(&adap->devnode.lock);
+	mutex_lock(&adap->devnode.lock_fhs);
 	list_for_each_entry(fh, &adap->devnode.fhs, list)
 		cec_queue_event_fh(fh, &ev, ktime_to_ns(ts));
-	mutex_unlock(&adap->devnode.lock);
+	mutex_unlock(&adap->devnode.lock_fhs);
 }
 EXPORT_SYMBOL_GPL(cec_queue_pin_hpd_event);
 
@@ -211,10 +212,10 @@ void cec_queue_pin_5v_event(struct cec_adapter *adap, bool is_high, ktime_t ts)
 	};
 	struct cec_fh *fh;
 
-	mutex_lock(&adap->devnode.lock);
+	mutex_lock(&adap->devnode.lock_fhs);
 	list_for_each_entry(fh, &adap->devnode.fhs, list)
 		cec_queue_event_fh(fh, &ev, ktime_to_ns(ts));
-	mutex_unlock(&adap->devnode.lock);
+	mutex_unlock(&adap->devnode.lock_fhs);
 }
 EXPORT_SYMBOL_GPL(cec_queue_pin_5v_event);
 
@@ -286,12 +287,12 @@ static void cec_queue_msg_monitor(struct cec_adapter *adap,
 	u32 monitor_mode = valid_la ? CEC_MODE_MONITOR :
 				      CEC_MODE_MONITOR_ALL;
 
-	mutex_lock(&adap->devnode.lock);
+	mutex_lock(&adap->devnode.lock_fhs);
 	list_for_each_entry(fh, &adap->devnode.fhs, list) {
 		if (fh->mode_follower >= monitor_mode)
 			cec_queue_msg_fh(fh, msg);
 	}
-	mutex_unlock(&adap->devnode.lock);
+	mutex_unlock(&adap->devnode.lock_fhs);
 }
 
 /*
@@ -302,12 +303,12 @@ static void cec_queue_msg_followers(struct cec_adapter *adap,
 {
 	struct cec_fh *fh;
 
-	mutex_lock(&adap->devnode.lock);
+	mutex_lock(&adap->devnode.lock_fhs);
 	list_for_each_entry(fh, &adap->devnode.fhs, list) {
 		if (fh->mode_follower == CEC_MODE_FOLLOWER)
 			cec_queue_msg_fh(fh, msg);
 	}
-	mutex_unlock(&adap->devnode.lock);
+	mutex_unlock(&adap->devnode.lock_fhs);
 }
 
 /* Notify userspace of an adapter state change. */
@@ -1578,6 +1579,7 @@ void __cec_s_phys_addr(struct cec_adapter *adap, u16 phys_addr, bool block)
 		/* Disabling monitor all mode should always succeed */
 		if (adap->monitor_all_cnt)
 			WARN_ON(call_op(adap, adap_monitor_all_enable, false));
+		/* serialize adap_enable */
 		mutex_lock(&adap->devnode.lock);
 		if (adap->needs_hpd || list_empty(&adap->devnode.fhs)) {
 			WARN_ON(adap->ops->adap_enable(adap, false));
@@ -1589,14 +1591,16 @@ void __cec_s_phys_addr(struct cec_adapter *adap, u16 phys_addr, bool block)
 			return;
 	}
 
+	/* serialize adap_enable */
 	mutex_lock(&adap->devnode.lock);
 	adap->last_initiator = 0xff;
 	adap->transmit_in_progress = false;
 
-	if ((adap->needs_hpd || list_empty(&adap->devnode.fhs)) &&
-	    adap->ops->adap_enable(adap, true)) {
-		mutex_unlock(&adap->devnode.lock);
-		return;
+	if (adap->needs_hpd || list_empty(&adap->devnode.fhs)) {
+		if (adap->ops->adap_enable(adap, true)) {
+			mutex_unlock(&adap->devnode.lock);
+			return;
+		}
 	}
 
 	if (adap->monitor_all_cnt &&
diff --git a/drivers/media/cec/core/cec-api.c b/drivers/media/cec/core/cec-api.c
index 0edb7142afdb..d72ad48c9898 100644
--- a/drivers/media/cec/core/cec-api.c
+++ b/drivers/media/cec/core/cec-api.c
@@ -586,6 +586,7 @@ static int cec_open(struct inode *inode, struct file *filp)
 		return err;
 	}
 
+	/* serialize adap_enable */
 	mutex_lock(&devnode->lock);
 	if (list_empty(&devnode->fhs) &&
 	    !adap->needs_hpd &&
@@ -624,7 +625,9 @@ static int cec_open(struct inode *inode, struct file *filp)
 	}
 #endif
 
+	mutex_lock(&devnode->lock_fhs);
 	list_add(&fh->list, &devnode->fhs);
+	mutex_unlock(&devnode->lock_fhs);
 	mutex_unlock(&devnode->lock);
 
 	return 0;
@@ -653,8 +656,11 @@ static int cec_release(struct inode *inode, struct file *filp)
 		cec_monitor_all_cnt_dec(adap);
 	mutex_unlock(&adap->lock);
 
+	/* serialize adap_enable */
 	mutex_lock(&devnode->lock);
+	mutex_lock(&devnode->lock_fhs);
 	list_del(&fh->list);
+	mutex_unlock(&devnode->lock_fhs);
 	if (cec_is_registered(adap) && list_empty(&devnode->fhs) &&
 	    !adap->needs_hpd && adap->phys_addr == CEC_PHYS_ADDR_INVALID) {
 		WARN_ON(adap->ops->adap_enable(adap, false));
diff --git a/drivers/media/cec/core/cec-core.c b/drivers/media/cec/core/cec-core.c
index 551689d371a7..ec67065d5202 100644
--- a/drivers/media/cec/core/cec-core.c
+++ b/drivers/media/cec/core/cec-core.c
@@ -169,8 +169,10 @@ static void cec_devnode_unregister(struct cec_adapter *adap)
 	devnode->registered = false;
 	devnode->unregistered = true;
 
+	mutex_lock(&devnode->lock_fhs);
 	list_for_each_entry(fh, &devnode->fhs, list)
 		wake_up_interruptible(&fh->wait);
+	mutex_unlock(&devnode->lock_fhs);
 
 	mutex_unlock(&devnode->lock);
 
@@ -272,6 +274,7 @@ struct cec_adapter *cec_allocate_adapter(const struct cec_adap_ops *ops,
 
 	/* adap->devnode initialization */
 	INIT_LIST_HEAD(&adap->devnode.fhs);
+	mutex_init(&adap->devnode.lock_fhs);
 	mutex_init(&adap->devnode.lock);
 
 	adap->kthread = kthread_run(cec_thread_func, adap, "cec-%s", name);
diff --git a/include/media/cec.h b/include/media/cec.h
index 208c9613c07e..77346f757036 100644
--- a/include/media/cec.h
+++ b/include/media/cec.h
@@ -26,13 +26,17 @@
  * @dev:	cec device
  * @cdev:	cec character device
  * @minor:	device node minor number
+ * @lock:	lock to serialize open/release and registration
  * @registered:	the device was correctly registered
  * @unregistered: the device was unregistered
+ * @lock_fhs:	lock to control access to @fhs
  * @fhs:	the list of open filehandles (cec_fh)
- * @lock:	lock to control access to this structure
  *
  * This structure represents a cec-related device node.
  *
+ * To add or remove filehandles from @fhs the @lock must be taken first,
+ * followed by @lock_fhs. It is safe to access @fhs if either lock is held.
+ *
  * The @parent is a physical device. It must be set by core or device drivers
  * before registering the node.
  */
@@ -43,10 +47,13 @@ struct cec_devnode {
 
 	/* device info */
 	int minor;
+	/* serialize open/release and registration */
+	struct mutex lock;
 	bool registered;
 	bool unregistered;
+	/* protect access to fhs */
+	struct mutex lock_fhs;
 	struct list_head fhs;
-	struct mutex lock;
 };
 
 struct cec_adapter;
-- 
2.33.0