linux-kernel - [PATCH] tty: hvcs: Don't NULL tty->driver_data until hvcs

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Date:   Thu, 20 Aug 2020 18:46:38 -0500
From:   Tyrel Datwyler <tyreld@...ux.ibm.com>
To:     gregkh@...uxfoundation.org
Cc:     Tyrel Datwyler <tyreld@...ux.ibm.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Jason Yan <yanaijie@...wei.com>, Joe Perches <joe@...ches.com>,
        linuxppc-dev@...ts.ozlabs.org (open list:HYPERVISOR VIRTUAL CONSOLE
        DRIVER), linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] tty: hvcs: Don't NULL tty->driver_data until hvcs_cleanup()

The code currently NULLs tty->driver_data in hvcs_close() with the
intent of informing the next call to hvcs_open() that device needs to be
reconfigured. However, when hvcs_cleanup() is called we copy hvcsd from
tty->driver_data which was previoulsy NULLed by hvcs_close() and our
call to tty_port_put(&hvcsd->port) doesn't actually do anything since
&hvcsd->port ends up translating to NULL by chance. This has the side
effect that when hvcs_remove() is called we have one too many port
references preventing hvcs_destuct_port() from ever being called. This
also prevents us from reusing the /dev/hvcsX node in a future
hvcs_probe() and we can eventually run out of /dev/hvcsX devices.

Fix this by waiting to NULL tty->driver_data in hvcs_cleanup().

Signed-off-by: Tyrel Datwyler <tyreld@...ux.ibm.com>
---
 drivers/tty/hvc/hvcs.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/tty/hvc/hvcs.c b/drivers/tty/hvc/hvcs.c
index 55105ac38f89..509d1042825a 100644
--- a/drivers/tty/hvc/hvcs.c
+++ b/drivers/tty/hvc/hvcs.c
@@ -1216,13 +1216,6 @@ static void hvcs_close(struct tty_struct *tty, struct file *filp)

 		tty_wait_until_sent(tty, HVCS_CLOSE_WAIT);

-		/*
-		 * This line is important because it tells hvcs_open that this
-		 * device needs to be re-configured the next time hvcs_open is
-		 * called.
-		 */
-		tty->driver_data = NULL;
-
 		free_irq(irq, hvcsd);
 		return;
 	} else if (hvcsd->port.count < 0) {
@@ -1237,6 +1230,13 @@ static void hvcs_cleanup(struct tty_struct * tty)
 {
 	struct hvcs_struct *hvcsd = tty->driver_data;

+	/*
+	 * This line is important because it tells hvcs_open that this
+	 * device needs to be re-configured the next time hvcs_open is
+	 * called.
+	 */
+	tty->driver_data = NULL;
+
 	tty_port_put(&hvcsd->port);
 }

-- 
2.27.0