serial: 8250: synchronize and annotate UART_IER access

The UART_IER register is modified twice by each console write
(serial8250_console_write()) under the port lock. Any driver code that
accesses UART_IER must do so with the port locked in order to ensure
consistent values, even when for read accesses.

Add locking, lockdep notation, and/or comments everywhere UART_IER is
accessed. The added locking is not fixing a real problem because it
occurs where the console is not active. However, adding the locking
to these non-critical paths greatly simplifies UART_IER access
tracking by establishing a general policy that all UART_IER access
is performed with the port locked.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Link: https://lore.kernel.org/r/20230525093159.223817-9-john.ogness@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index 5418708..471c6bc 100644 (file)
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h
@@ -179,6 +179,9 @@ static inline void serial_dl_write(struct uart_8250_port *up, u32 value)
 
 static inline bool serial8250_set_THRI(struct uart_8250_port *up)
 {
+       /* Port locked to synchronize UART_IER access against the console. */
+       lockdep_assert_held_once(&up->port.lock);
+
        if (up->ier & UART_IER_THRI)
                return false;
        up->ier |= UART_IER_THRI;
@@ -188,6 +191,9 @@ static inline bool serial8250_set_THRI(struct uart_8250_port *up)
 
 static inline bool serial8250_clear_THRI(struct uart_8250_port *up)
 {
+       /* Port locked to synchronize UART_IER access against the console. */
+       lockdep_assert_held_once(&up->port.lock);
+
        if (!(up->ier & UART_IER_THRI))
                return false;
        up->ier &= ~UART_IER_THRI;

diff --git a/drivers/tty/serial/8250/8250_aspeed_vuart.c b/drivers/tty/serial/8250/8250_aspeed_vuart.c
index 9d2a785..4a9e71b 100644 (file)
--- a/drivers/tty/serial/8250/8250_aspeed_vuart.c
+++ b/drivers/tty/serial/8250/8250_aspeed_vuart.c
@@ -275,6 +275,9 @@ static void __aspeed_vuart_set_throttle(struct uart_8250_port *up,
 {
        unsigned char irqs = UART_IER_RLSI | UART_IER_RDI;
 
+       /* Port locked to synchronize UART_IER access against the console. */
+       lockdep_assert_held_once(&up->port.lock);
+
        up->ier &= ~irqs;
        if (!throttle)
                up->ier |= irqs;

diff --git a/drivers/tty/serial/8250/8250_mtk.c b/drivers/tty/serial/8250/8250_mtk.c
index fb1d5ec..aa8e981 100644 (file)
--- a/drivers/tty/serial/8250/8250_mtk.c
+++ b/drivers/tty/serial/8250/8250_mtk.c
@@ -222,11 +222,17 @@ static void mtk8250_shutdown(struct uart_port *port)
 
 static void mtk8250_disable_intrs(struct uart_8250_port *up, int mask)
 {
+       /* Port locked to synchronize UART_IER access against the console. */
+       lockdep_assert_held_once(&up->port.lock);
+
        serial_out(up, UART_IER, serial_in(up, UART_IER) & (~mask));
 }
 
 static void mtk8250_enable_intrs(struct uart_8250_port *up, int mask)
 {
+       /* Port locked to synchronize UART_IER access against the console. */
+       lockdep_assert_held_once(&up->port.lock);
+
        serial_out(up, UART_IER, serial_in(up, UART_IER) | mask);
 }
 
@@ -235,6 +241,9 @@ static void mtk8250_set_flow_ctrl(struct uart_8250_port *up, int mode)
        struct uart_port *port = &up->port;
        int lcr = serial_in(up, UART_LCR);
 
+       /* Port locked to synchronize UART_IER access against the console. */
+       lockdep_assert_held_once(&port->lock);
+
        serial_out(up, UART_LCR, UART_LCR_CONF_MODE_B);
        serial_out(up, MTK_UART_EFR, UART_EFR_ECB);
        serial_out(up, UART_LCR, lcr);

diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
index 3225c95..0498b9b 100644 (file)
--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c
@@ -533,6 +533,10 @@ static void omap_8250_pm(struct uart_port *port, unsigned int state,
        u8 efr;
 
        pm_runtime_get_sync(port->dev);
+
+       /* Synchronize UART_IER access against the console. */
+       spin_lock_irq(&port->lock);
+
        serial_out(up, UART_LCR, UART_LCR_CONF_MODE_B);
        efr = serial_in(up, UART_EFR);
        serial_out(up, UART_EFR, efr | UART_EFR_ECB);
@@ -543,6 +547,8 @@ static void omap_8250_pm(struct uart_port *port, unsigned int state,
        serial_out(up, UART_EFR, efr);
        serial_out(up, UART_LCR, 0);
 
+       spin_unlock_irq(&port->lock);
+
        pm_runtime_mark_last_busy(port->dev);
        pm_runtime_put_autosuspend(port->dev);
 }
@@ -760,8 +766,11 @@ static void omap_8250_shutdown(struct uart_port *port)
        if (priv->habit & UART_HAS_EFR2)
                serial_out(up, UART_OMAP_EFR2, 0x0);
 
+       /* Synchronize UART_IER access against the console. */
+       spin_lock_irq(&port->lock);
        up->ier = 0;
        serial_out(up, UART_IER, 0);
+       spin_unlock_irq(&port->lock);
        disable_irq_nosync(up->port.irq);
        dev_pm_clear_wake_irq(port->dev);
 
@@ -803,6 +812,7 @@ static void omap_8250_unthrottle(struct uart_port *port)
 
        pm_runtime_get_sync(port->dev);
 
+       /* Synchronize UART_IER access against the console. */
        spin_lock_irqsave(&port->lock, flags);
        priv->throttled = false;
        if (up->dma)
@@ -953,6 +963,7 @@ static void __dma_rx_complete(void *param)
        struct dma_tx_state     state;
        unsigned long flags;
 
+       /* Synchronize UART_IER access against the console. */
        spin_lock_irqsave(&p->port.lock, flags);
 
        /*
@@ -1227,6 +1238,9 @@ static u16 omap_8250_handle_rx_dma(struct uart_8250_port *up, u8 iir, u16 status
 static void am654_8250_handle_rx_dma(struct uart_8250_port *up, u8 iir,
                                     u16 status)
 {
+       /* Port locked to synchronize UART_IER access against the console. */
+       lockdep_assert_held_once(&up->port.lock);
+
        /*
         * Queue a new transfer if FIFO has data.
         */

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index ecfcdc0..1321bb4 100644 (file)
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -539,6 +539,9 @@ EXPORT_SYMBOL_GPL(serial8250_rpm_put);
  */
 static int serial8250_em485_init(struct uart_8250_port *p)
 {
+       /* Port locked to synchronize UART_IER access against the console. */
+       lockdep_assert_held_once(&p->port.lock);
+
        if (p->em485)
                goto deassert_rts;
 
@@ -677,6 +680,8 @@ static void serial8250_set_sleep(struct uart_8250_port *p, int sleep)
        serial8250_rpm_get(p);
 
        if (p->capabilities & UART_CAP_SLEEP) {
+               /* Synchronize UART_IER access against the console. */
+               spin_lock_irq(&p->port.lock);
                if (p->capabilities & UART_CAP_EFR) {
                        lcr = serial_in(p, UART_LCR);
                        efr = serial_in(p, UART_EFR);
@@ -690,6 +695,7 @@ static void serial8250_set_sleep(struct uart_8250_port *p, int sleep)
                        serial_out(p, UART_EFR, efr);
                        serial_out(p, UART_LCR, lcr);
                }
+               spin_unlock_irq(&p->port.lock);
        }
 
        serial8250_rpm_put(p);
@@ -697,6 +703,9 @@ static void serial8250_set_sleep(struct uart_8250_port *p, int sleep)
 
 static void serial8250_clear_IER(struct uart_8250_port *up)
 {
+       /* Port locked to synchronize UART_IER access against the console. */
+       lockdep_assert_held_once(&up->port.lock);
+
        if (up->capabilities & UART_CAP_UUE)
                serial_out(up, UART_IER, UART_IER_UUE);
        else
@@ -969,6 +978,9 @@ static void autoconfig_16550a(struct uart_8250_port *up)
        unsigned char status1, status2;
        unsigned int iersave;
 
+       /* Port locked to synchronize UART_IER access against the console. */
+       lockdep_assert_held_once(&up->port.lock);
+
        up->port.type = PORT_16550A;
        up->capabilities |= UART_CAP_FIFO;
 
@@ -1152,6 +1164,8 @@ static void autoconfig(struct uart_8250_port *up)
        /*
         * We really do need global IRQs disabled here - we're going to
         * be frobbing the chips IRQ enable register to see if it exists.
+        *
+        * Synchronize UART_IER access against the console.
         */
        spin_lock_irqsave(&port->lock, flags);
 
@@ -1324,7 +1338,10 @@ static void autoconfig_irq(struct uart_8250_port *up)
        /* forget possible initially masked and pending IRQ */
        probe_irq_off(probe_irq_on());
        save_mcr = serial8250_in_MCR(up);
+       /* Synchronize UART_IER access against the console. */
+       spin_lock_irq(&port->lock);
        save_ier = serial_in(up, UART_IER);
+       spin_unlock_irq(&port->lock);
        serial8250_out_MCR(up, UART_MCR_OUT1 | UART_MCR_OUT2);
 
        irqs = probe_irq_on();
@@ -1336,7 +1353,10 @@ static void autoconfig_irq(struct uart_8250_port *up)
                serial8250_out_MCR(up,
                        UART_MCR_DTR | UART_MCR_RTS | UART_MCR_OUT2);
        }
+       /* Synchronize UART_IER access against the console. */
+       spin_lock_irq(&port->lock);
        serial_out(up, UART_IER, UART_IER_ALL_INTR);
+       spin_unlock_irq(&port->lock);
        serial_in(up, UART_LSR);
        serial_in(up, UART_RX);
        serial_in(up, UART_IIR);
@@ -1346,7 +1366,10 @@ static void autoconfig_irq(struct uart_8250_port *up)
        irq = probe_irq_off(irqs);
 
        serial8250_out_MCR(up, save_mcr);
+       /* Synchronize UART_IER access against the console. */
+       spin_lock_irq(&port->lock);
        serial_out(up, UART_IER, save_ier);
+       spin_unlock_irq(&port->lock);
 
        if (port->flags & UPF_FOURPORT)
                outb_p(save_ICP, ICP);
@@ -1361,6 +1384,9 @@ static void serial8250_stop_rx(struct uart_port *port)
 {
        struct uart_8250_port *up = up_to_u8250p(port);
 
+       /* Port locked to synchronize UART_IER access against the console. */
+       lockdep_assert_held_once(&port->lock);
+
        serial8250_rpm_get(up);
 
        up->ier &= ~(UART_IER_RLSI | UART_IER_RDI);
@@ -1380,6 +1406,9 @@ void serial8250_em485_stop_tx(struct uart_8250_port *p)
 {
        unsigned char mcr = serial8250_in_MCR(p);
 
+       /* Port locked to synchronize UART_IER access against the console. */
+       lockdep_assert_held_once(&p->port.lock);
+
        if (p->port.rs485.flags & SER_RS485_RTS_AFTER_SEND)
                mcr |= UART_MCR_RTS;
        else
@@ -1429,6 +1458,9 @@ static void __stop_tx_rs485(struct uart_8250_port *p, u64 stop_delay)
 {
        struct uart_8250_em485 *em485 = p->em485;
 
+       /* Port locked to synchronize UART_IER access against the console. */
+       lockdep_assert_held_once(&p->port.lock);
+
        stop_delay += (u64)p->port.rs485.delay_rts_after_send * NSEC_PER_MSEC;
 
        /*
@@ -1608,6 +1640,9 @@ static void serial8250_start_tx(struct uart_port *port)
        struct uart_8250_port *up = up_to_u8250p(port);
        struct uart_8250_em485 *em485 = up->em485;
 
+       /* Port locked to synchronize UART_IER access against the console. */
+       lockdep_assert_held_once(&port->lock);
+
        if (!port->x_char && uart_circ_empty(&port->state->xmit))
                return;
 
@@ -1635,6 +1670,9 @@ static void serial8250_disable_ms(struct uart_port *port)
 {
        struct uart_8250_port *up = up_to_u8250p(port);
 
+       /* Port locked to synchronize UART_IER access against the console. */
+       lockdep_assert_held_once(&port->lock);
+
        /* no MSR capabilities */
        if (up->bugs & UART_BUG_NOMSR)
                return;
@@ -1649,6 +1687,9 @@ static void serial8250_enable_ms(struct uart_port *port)
 {
        struct uart_8250_port *up = up_to_u8250p(port);
 
+       /* Port locked to synchronize UART_IER access against the console. */
+       lockdep_assert_held_once(&port->lock);
+
        /* no MSR capabilities */
        if (up->bugs & UART_BUG_NOMSR)
                return;
@@ -2105,6 +2146,14 @@ static void serial8250_put_poll_char(struct uart_port *port,
        unsigned int ier;
        struct uart_8250_port *up = up_to_u8250p(port);
 
+       /*
+        * Normally the port is locked to synchronize UART_IER access
+        * against the console. However, this function is only used by
+        * KDB/KGDB, where it may not be possible to acquire the port
+        * lock because all other CPUs are quiesced. The quiescence
+        * should allow safe lockless usage here.
+        */
+
        serial8250_rpm_get(up);
        /*
         *      First save the IER then disable the interrupts
@@ -2440,6 +2489,8 @@ void serial8250_do_shutdown(struct uart_port *port)
        serial8250_rpm_get(up);
        /*
         * Disable interrupts from this port
+        *
+        * Synchronize UART_IER access against the console.
         */
        spin_lock_irqsave(&port->lock, flags);
        up->ier = 0;
@@ -2739,6 +2790,8 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
        /*
         * Ok, we're now changing the port state.  Do it with
         * interrupts disabled.
+        *
+        * Synchronize UART_IER access against the console.
         */
        serial8250_rpm_get(up);
        spin_lock_irqsave(&port->lock, flags);