tty: mxser: drop low-latency workaround

Commit 67d2bc58afdd ("Char: mxser_new, fix recursive locking") worked
around the infamous low_latency behaviour of tty_flip_buffer_push() by
simply dropping and reacquiring the port lock in the interrupt handler.

Since commit a9c3f68f3cd8 ("tty: Fix low_latency BUG"),
tty_flip_buffer_push() always schedules a work item to push data to the
line discipline and there's no need to keep any low_latency hacks around.

Link: https://lore.kernel.org/lkml/3018694794025219@wsc.cz/T/#m06b04c640a7b6f41afb3d34a4cf29b1df4935d3a
Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20210421095509.3024-2-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/mxser.c b/drivers/tty/mxser.c
index 2d8e76263a25be298c760dcdc32029998f6117af..16a852ecbe8a6a4e3ce2ff610dfd6cfd29d03405 100644 (file)
--- a/drivers/tty/mxser.c
+++ b/drivers/tty/mxser.c
@@ -2155,14 +2155,7 @@ end_intr:
        port->mon_data.rxcnt += cnt;
        port->mon_data.up_rxcnt += cnt;
 
-       /*
-        * We are called from an interrupt context with &port->slock
-        * being held. Drop it temporarily in order to prevent
-        * recursive locking.
-        */
-       spin_unlock(&port->slock);
        tty_flip_buffer_push(&port->port);
-       spin_lock(&port->slock);
 }
 
 static void mxser_transmit_chars(struct tty_struct *tty, struct mxser_port *port)