USB: cdc-acm: fix break reporting

This fixes a couple of bugs in the recently added support for reporting break events.

Note that the offending commit was backported to stable.

Johan

Johan Hovold (2):
USB: cdc-acm: fix racy tty buffer accesses
USB: cdc-acm: fix break detection

 drivers/usb/class/cdc-acm.c | 8 ++++++++
 1 file changed, 8 insertions(+)

2.32.0

A recent change that started reporting break events to the line discipline caused the tty-buffer insertions to no longer be serialised by inserting events also from the completion handler for the interrupt endpoint.

Completion calls for distinct endpoints are not guaranteed to be serialised. For example, in case a host-controller driver uses bottom-half completion, the interrupt and bulk-in completion handlers can end up running in parallel on two CPUs (high-and low-prio tasklets, respectively) thereby breaking the tty layer's single producer assumption.

Fix this by holding the read lock also when inserting characters from the bulk endpoint.

---
 drivers/usb/class/cdc-acm.c | 5 +++++
 1 file changed, 5 insertions(+)

index 4e2f1552f4b7..c7a1736720e7 100644
@@ -475,11 +475,16 @@ static int acm_submit_read_urbs(struct acm *acm, gfp_t mem_flags)
 
 static void acm_process_read_urb(struct acm *acm, struct urb *urb)
 {
+	unsigned long flags;
+
 	if (!urb->actual_length)
 		return;
 
+	spin_lock_irqsave(&acm->read_lock, flags);
 	tty_insert_flip_string(&acm->port, urb->transfer_buffer,
 			urb->actual_length);
+	spin_unlock_irqrestore(&acm->read_lock, flags);
+
 	tty_flip_buffer_push(&acm->port);
 }
 

2.32.0

A recent change that started reporting break events forgot to push the event to the line discipline, which meant that a detected break would not be reported until further characters had been receive (the port could even have been closed and reopened in between).

---
 drivers/usb/class/cdc-acm.c | 3 +++
 1 file changed, 3 insertions(+)

index c7a1736720e7..7b2e2420ecae 100644
@@ -340,6 +340,9 @@ static void acm_process_notification(struct acm *acm, unsigned char *buf)
 			acm->iocount.overrun++;
 		spin_unlock_irqrestore(&acm->read_lock, flags);
 
+		if (newctrl & ACM_CTRL_BRK)
+			tty_flip_buffer_push(&acm->port);
+
 		if (difference)
 			wake_up_all(&acm->wioctl);
 

2.32.0