[PATCH] Input: serport - defer write wakeups to a worker
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DORMANTno replies
From: James Hilliard <james.hilliard1@gmail.com>
Date: 2026-10-24 04:23:48
Also in:
linux-serial, lkml
Subsystem:
input (keyboard, mouse, joystick, touchscreen) drivers, the rest · Maintainers:
Dmitry Torokhov, Linus Torvalds
UART drivers can invoke the line discipline's write_wakeup() callback with their port lock held. serport forwards the notification directly to the serio driver. I-Force's callback can transmit a queued packet through serio_write(), which calls back into uart_write() and tries to acquire the same port lock. A notification after I-Force queues a packet but before it sets IFORCE_XMIT_RUNNING can therefore deadlock. Defer the serio notification to a work item, as required for transmitting from a line discipline's write-wakeup path. Keep the SERPORT_ACTIVE check and callback under serport->lock to serialize with serio close. Cancel the work before freeing serport in line-discipline close, where the TTY layer has already excluded further line-discipline callbacks. Signed-off-by: James Hilliard <james.hilliard1@gmail.com> --- drivers/input/serio/serport.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-)
diff --git a/drivers/input/serio/serport.c b/drivers/input/serio/serport.c
index cabe3876c168..24c0d0c0c9aa 100644
--- a/drivers/input/serio/serport.c
+++ b/drivers/input/serio/serport.c@@ -18,6 +18,7 @@ #include <linux/serio.h> #include <linux/tty.h> #include <linux/compat.h> +#include <linux/workqueue.h> MODULE_AUTHOR("Vojtech Pavlik <vojtech@ucw.cz>"); MODULE_DESCRIPTION("Input device TTY line discipline");
@@ -33,6 +34,7 @@ struct serport { wait_queue_head_t wait; struct serio *serio; struct serio_device_id id; + struct work_struct write_wakeup; spinlock_t lock; unsigned long flags; };
@@ -66,6 +68,16 @@ static void serport_serio_close(struct serio *serio) clear_bit(SERPORT_ACTIVE, &serport->flags); } +static void serport_write_wakeup(struct work_struct *work) +{ + struct serport *serport = container_of(work, struct serport, write_wakeup); + + guard(spinlock_irqsave)(&serport->lock); + + if (test_bit(SERPORT_ACTIVE, &serport->flags)) + serio_drv_write_wakeup(serport->serio); +} + /* * serport_ldisc_open() is the routine that is called upon setting our line * discipline on a tty. It prepares the serio struct.
@@ -85,6 +97,7 @@ static int serport_ldisc_open(struct tty_struct *tty) serport->tty = tty; spin_lock_init(&serport->lock); init_waitqueue_head(&serport->wait); + INIT_WORK(&serport->write_wakeup, serport_write_wakeup); tty->disc_data = serport; tty->receive_room = 256;
@@ -101,6 +114,7 @@ static void serport_ldisc_close(struct tty_struct *tty) { struct serport *serport = tty->disc_data; + cancel_work_sync(&serport->write_wakeup); kfree(serport); }
@@ -249,10 +263,8 @@ static void serport_ldisc_write_wakeup(struct tty_struct * tty) { struct serport *serport = tty->disc_data; - guard(spinlock_irqsave)(&serport->lock); - - if (test_bit(SERPORT_ACTIVE, &serport->flags)) - serio_drv_write_wakeup(serport->serio); + /* A serio driver may write to the TTY, so defer the callback. */ + schedule_work(&serport->write_wakeup); } /*
--- base-commit: 2e6f2e5799f328ca0879dad14d7f3709c7f7496b change-id: 20261023-submit-serport-write-wakeup-v1-1bdd1006fafa Best regards, -- James Hilliard [off-list ref]