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serial: 8250: synchronize and annotate UART_IER access
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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>
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John Ogness authored and Greg Kroah-Hartman committed May 30, 2023
1 parent 2561473 commit d0b309a
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Showing 5 changed files with 85 additions and 0 deletions.
6 changes: 6 additions & 0 deletions drivers/tty/serial/8250/8250.h
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand All @@ -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;
Expand Down
3 changes: 3 additions & 0 deletions drivers/tty/serial/8250/8250_aspeed_vuart.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down
9 changes: 9 additions & 0 deletions drivers/tty/serial/8250/8250_mtk.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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);
}

Expand All @@ -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);
Expand Down
14 changes: 14 additions & 0 deletions drivers/tty/serial/8250/8250_omap.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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);
Expand All @@ -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);
}
Expand Down Expand Up @@ -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);

Expand Down Expand Up @@ -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)
Expand Down Expand Up @@ -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);

/*
Expand Down Expand Up @@ -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.
*/
Expand Down
53 changes: 53 additions & 0 deletions drivers/tty/serial/8250/8250_port.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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;

Expand Down Expand Up @@ -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);
Expand All @@ -690,13 +695,17 @@ 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);
}

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
Expand Down Expand Up @@ -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;

Expand Down Expand Up @@ -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);

Expand Down Expand Up @@ -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();
Expand All @@ -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);
Expand All @@ -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);
Expand All @@ -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);
Expand All @@ -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
Expand Down Expand Up @@ -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;

/*
Expand Down Expand Up @@ -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;

Expand Down Expand Up @@ -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;
Expand All @@ -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;
Expand Down Expand Up @@ -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
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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);
Expand Down

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