patch "tty: serial: imx: fix potential deadlock" added to tty-linus

This is a note to let you know that I've just added the patch titled

tty: serial: imx: fix potential deadlock

to my tty git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git
in the tty-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From 33f16855dcb973f745c51882d0e286601ff3be2b Mon Sep 17 00:00:00 2001
From: Sam Nobs <[email protected]>
Date: Tue, 10 Nov 2020 09:50:06 +1300
Subject: tty: serial: imx: fix potential deadlock
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Enabling the lock dependency validator has revealed that the way spinlocks are used in the IMX serial port could result in a deadlock.

Specifically, imx_uart_int() acquires a spinlock without disabling the interrupts, meaning that another interrupt could come along and try to acquire the same spinlock, potentially causing the two to wait for each other indefinitely.

Use spin_lock_irqsave() instead to disable interrupts upon acquisition of the spinlock.

Fixes c974991d2620 ("tty:serial:imx: use spin_lock instead of spin_lock_irqsave in isr")

Reviewed-by Uwe Kleine-König <[email protected]>

Signed-off-by Sam Nobs <[email protected]>

Link https://lore.kernel.org/r/[email protected] open here

Cc stable <[email protected]>

Signed-off-by Greg Kroah-Hartman <[email protected]>

---
 drivers/tty/serial/imx.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

drivers/tty/serial/imx.c +8 -3

index 1731d9728865..3c53a3c89959 100644
@@ -942,8 +942,14 @@ static irqreturn_t imx_uart_int(int irq, void *dev_id)
        struct imx_port *sport = dev_id;
        unsigned int usr1, usr2, ucr1, ucr2, ucr3, ucr4;
        irqreturn_t ret = IRQ_NONE;
+       unsigned long flags = 0;
 
-       spin_lock(&sport->port.lock);
+       /*
+        * IRQs might not be disabled upon entering this interrupt handler,
+        * e.g. when interrupt handlers are forced to be threaded. To support
+        * this scenario as well, disable IRQs when acquiring the spinlock.
+        */
+       spin_lock_irqsave(&sport->port.lock, flags);
 
        usr1 = imx_uart_readl(sport, USR1);
        usr2 = imx_uart_readl(sport, USR2);

@@ -1013,7 +1019,7 @@ static irqreturn_t imx_uart_int(int irq, void *dev_id)
                ret = IRQ_HANDLED;
        }
 
-       spin_unlock(&sport->port.lock);
+       spin_unlock_irqrestore(&sport->port.lock, flags);
 
        return ret;
 }
--

2.29.2