serial: 8250: fix handle_irq locking

The 8250 handle_irq callback is not just called from the interrupt
handler but also from a timer callback when polling (e.g. for ports
without an interrupt line). Consequently the callback must explicitly
disable interrupts to avoid a potential deadlock with another interrupt
in polled mode.

Add back an irqrestore-version of the sysrq port-unlock helper and use
it in the 8250 callbacks that need it.

Fixes: 75f4e830fa9c ("serial: do not restore interrupt state in sysrq helper")
Cc: stable@vger.kernel.org	# 5.13
Cc: Joel Stanley <joel@jms.id.au>
Cc: Andrew Jeffery <andrew@aj.id.au>
Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20210714080427.28164-1-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/8250/8250_aspeed_vuart.c b/drivers/tty/serial/8250/8250_aspeed_vuart.c
index 4caab87..2350fb3 100644 (file)
--- a/drivers/tty/serial/8250/8250_aspeed_vuart.c
+++ b/drivers/tty/serial/8250/8250_aspeed_vuart.c
@@ -329,6 +329,7 @@ static int aspeed_vuart_handle_irq(struct uart_port *port)
 {
        struct uart_8250_port *up = up_to_u8250p(port);
        unsigned int iir, lsr;
+       unsigned long flags;
        unsigned int space, count;
 
        iir = serial_port_in(port, UART_IIR);
@@ -336,7 +337,7 @@ static int aspeed_vuart_handle_irq(struct uart_port *port)
        if (iir & UART_IIR_NO_INT)
                return 0;
 
-       spin_lock(&port->lock);
+       spin_lock_irqsave(&port->lock, flags);
 
        lsr = serial_port_in(port, UART_LSR);
 
@@ -370,7 +371,7 @@ static int aspeed_vuart_handle_irq(struct uart_port *port)
        if (lsr & UART_LSR_THRE)
                serial8250_tx_chars(up);
 
-       uart_unlock_and_check_sysrq(port);
+       uart_unlock_and_check_sysrq_irqrestore(port, flags);
 
        return 1;
 }

diff --git a/drivers/tty/serial/8250/8250_fsl.c b/drivers/tty/serial/8250/8250_fsl.c
index 4e75d2e..fc65a22 100644 (file)
--- a/drivers/tty/serial/8250/8250_fsl.c
+++ b/drivers/tty/serial/8250/8250_fsl.c
@@ -30,10 +30,11 @@ struct fsl8250_data {
 int fsl8250_handle_irq(struct uart_port *port)
 {
        unsigned char lsr, orig_lsr;
+       unsigned long flags;
        unsigned int iir;
        struct uart_8250_port *up = up_to_u8250p(port);
 
-       spin_lock(&up->port.lock);
+       spin_lock_irqsave(&up->port.lock, flags);
 
        iir = port->serial_in(port, UART_IIR);
        if (iir & UART_IIR_NO_INT) {
@@ -82,7 +83,7 @@ int fsl8250_handle_irq(struct uart_port *port)
 
        up->lsr_saved_flags = orig_lsr;
 
-       uart_unlock_and_check_sysrq(&up->port);
+       uart_unlock_and_check_sysrq_irqrestore(&up->port, flags);
 
        return 1;
 }

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 2e7000f..1da29a2 100644 (file)
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1899,11 +1899,12 @@ int serial8250_handle_irq(struct uart_port *port, unsigned int iir)
        unsigned char status;
        struct uart_8250_port *up = up_to_u8250p(port);
        bool skip_rx = false;
+       unsigned long flags;
 
        if (iir & UART_IIR_NO_INT)
                return 0;
 
-       spin_lock(&port->lock);
+       spin_lock_irqsave(&port->lock, flags);
 
        status = serial_port_in(port, UART_LSR);
 
@@ -1929,7 +1930,7 @@ int serial8250_handle_irq(struct uart_port *port, unsigned int iir)
                (up->ier & UART_IER_THRI))
                serial8250_tx_chars(up);
 
-       uart_unlock_and_check_sysrq(port);
+       uart_unlock_and_check_sysrq_irqrestore(port, flags);
 
        return 1;
 }

diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 52d7fb9..c58cc14 100644 (file)
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -518,6 +518,25 @@ static inline void uart_unlock_and_check_sysrq(struct uart_port *port)
        if (sysrq_ch)
                handle_sysrq(sysrq_ch);
 }
+
+static inline void uart_unlock_and_check_sysrq_irqrestore(struct uart_port *port,
+               unsigned long flags)
+{
+       int sysrq_ch;
+
+       if (!port->has_sysrq) {
+               spin_unlock_irqrestore(&port->lock, flags);
+               return;
+       }
+
+       sysrq_ch = port->sysrq_ch;
+       port->sysrq_ch = 0;
+
+       spin_unlock_irqrestore(&port->lock, flags);
+
+       if (sysrq_ch)
+               handle_sysrq(sysrq_ch);
+}
 #else  /* CONFIG_MAGIC_SYSRQ_SERIAL */
 static inline int uart_handle_sysrq_char(struct uart_port *port, unsigned int ch)
 {
@@ -531,6 +550,11 @@ static inline void uart_unlock_and_check_sysrq(struct uart_port *port)
 {
        spin_unlock(&port->lock);
 }
+static inline void uart_unlock_and_check_sysrq_irqrestore(struct uart_port *port,
+               unsigned long flags)
+{
+       spin_unlock_irqrestore(&port->lock, flags);
+}
 #endif /* CONFIG_MAGIC_SYSRQ_SERIAL */
 
 /*