With CONFIG_PREEMPT_RT_FULL the tty_flip_buffer_push(..) actions are executed
immeditely (same behaviour as if low_latency flag was set). We thus have to
release port_lock before callng tty_flip_buffer_push().
This issue resultst of commits:
44a0c019: USB: g_serial: don't set low_latency flag
dc0cbd1b: serial: 8250: Call flush_to_ldisc when the irq is threaded
Signed-off-by: Jean-Jacques Hiblot <jjhiblot@xxxxxxxxxxxxxxx>
---
changes since v1:
- fix compilation problem: use port.tty instead of port->port_tty
drivers/usb/gadget/u_serial.c | 23 ++++++++++++++++++-----
1 file changed, 18 insertions(+), 5 deletions(-)
diff --git a/drivers/usb/gadget/u_serial.c b/drivers/usb/gadget/u_serial.c
index b369292..3d4246d 100644
--- a/drivers/usb/gadget/u_serial.c
+++ b/drivers/usb/gadget/u_serial.c
@@ -549,12 +549,25 @@ static void gs_rx_push(unsigned long _port)
port->read_started--;
}
- /* Push from tty to ldisc; without low_latency set this is handled by
- * a workqueue, so we won't get callbacks and can hold port_lock
- */
- if (do_push)
+ /* Push from tty to ldisc */
+ if (do_push) {
+#ifndef CONFIG_PREEMPT_RT_FULL
+ /* without low_latency set this is handled by a workqueue, so
+ * we won't get callbacks and can hold port_lock
+ */
tty_flip_buffer_push(&port->port);
-
+#else
+ /* CONFIG_PREEMPT_RT_FULL makes this a synchronous action. and
+ * it may trigger synchronous callbacks to this driver. We need
+ * to release the lock.
+ */
+ spin_unlock_irq(&port->port_lock);
+ tty_flip_buffer_push(&port->port);
+ spin_lock_irq(&port->port_lock);
+ /* tty may have been closed */
+ tty = port->port.tty;
+#endif
+ }
/* We want our data queue to become empty ASAP, keeping data
* in the tty and ldisc (not here). If we couldn't push any
--
1.9.2
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