linux-kernel - [PATCH] serial: altera_uart: fix locking in polling mode

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Message-Id: <20221122200426.888349-1-gsomlo@gmail.com>
Date:   Tue, 22 Nov 2022 15:04:26 -0500
From:   Gabriel Somlo <gsomlo@...il.com>
To:     linux-serial@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, tklauser@...tanz.ch,
        gregkh@...uxfoundation.org, jirislaby@...nel.org,
        cbouatmailru@...il.com, geert@...ux-m68k.org
Subject: [PATCH] serial: altera_uart: fix locking in polling mode

Since altera_uart_interrupt() may also be called from
a poll timer in "serving_softirq" context, use
spin_[lock_irqsave|unlock_irqrestore] variants, which
are appropriate for both softirq and hardware interrupt
contexts.

Fixes: 2f8b9c15cd88 ("altera_uart: Add support for polling mode (IRQ-less)")
Signed-off-by: Gabriel Somlo <gsomlo@...il.com>
---

I used this driver as a sorce of inspiration for adding IRQ support to
the LiteX LiteUART, and this topic came up during review. So I thought
it might be helpful to fix it here as well!

 drivers/tty/serial/altera_uart.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/altera_uart.c b/drivers/tty/serial/altera_uart.c
index 316074bb23e9..9ce3d24af536 100644
--- a/drivers/tty/serial/altera_uart.c
+++ b/drivers/tty/serial/altera_uart.c
@@ -259,16 +259,17 @@ static irqreturn_t altera_uart_interrupt(int irq, void *data)
 {
 	struct uart_port *port = data;
 	struct altera_uart *pp = container_of(port, struct altera_uart, port);
+	unsigned long flags;
 	unsigned int isr;
 
 	isr = altera_uart_readl(port, ALTERA_UART_STATUS_REG) & pp->imr;
 
-	spin_lock(&port->lock);
+	spin_lock_irqsave(&port->lock, flags);
 	if (isr & ALTERA_UART_STATUS_RRDY_MSK)
 		altera_uart_rx_chars(port);
 	if (isr & ALTERA_UART_STATUS_TRDY_MSK)
 		altera_uart_tx_chars(port);
-	spin_unlock(&port->lock);
+	spin_unlock_irqrestore(&port->lock, flags);
 
 	return IRQ_RETVAL(isr);
 }
-- 
2.38.1