[PATCH 5.11 150/601] serial: stm32: fix a deadlock condition with wakeup event

Greg Kroah-Hartman
2021-05-12T17:13:35Z

From: Erwan Le Ray <erwan.leray@foss.st.com>

[ Upstream commit ad7676812437a00a4c6be155fc17926069f99084 ]

Deadlock issue is seen when enabling CONFIG_PROVE_LOCKING=Y, and uart
console as wakeup source. Deadlock occurs when resuming from low power
mode if system is waked up via usart console.
The deadlock is triggered 100% when also disabling console suspend prior
to go to suspend.

Simplified call stack, deadlock condition:
- stm32_console_write <-- spin_lock already held
- print_circular_bug
- pm_wakeup_dev_event <-- triggers lockdep as seen above
- stm32_receive_chars
- stm32_interrupt <-- wakeup via uart console, takes the lock

So, revisit spin_lock in stm32-usart driver:
- there is no need to hold the lock to access ICR (atomic clear of status
flags)
- only hold the lock inside stm32_receive_chars() routine (no need to
call pm_wakeup_dev_event with lock held)
- keep stm32_transmit_chars() routine called with lock held

Fixes: 48a6092fb41f ("serial: stm32-usart: Add STM32 USART Driver")
Signed-off-by: Erwan Le Ray <erwan.leray@foss.st.com>
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Link: https://lore.kernel.org/r/20210304162308.8984-6-erwan.leray@foss.st.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/tty/serial/stm32-usart.c | 27 +++++++++++++++------------
1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 91a33ec4dbb4..5ae3841a4a08 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -213,13 +213,18 @@ static void stm32_usart_receive_chars(struct uart_port *port, bool threaded)
struct tty_port *tport = &port->state->port;
struct stm32_port *stm32_port = to_stm32_port(port);
const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
- unsigned long c;
+ unsigned long c, flags;
u32 sr;
char flag;

if (irqd_is_wakeup_set(irq_get_irq_data(port->irq)))
pm_wakeup_event(tport->tty->dev, 0);

+ if (threaded)
+ spin_lock_irqsave(&port->lock, flags);
+ else
+ spin_lock(&port->lock);
+
while (stm32_usart_pending_rx(port, &sr, &stm32_port->last_res,
threaded)) {
sr |= USART_SR_DUMMY_RX;
@@ -275,9 +280,12 @@ static void stm32_usart_receive_chars(struct uart_port *port, bool threaded)
uart_insert_char(port, sr, USART_SR_ORE, c, flag);
}

- spin_unlock(&port->lock);
+ if (threaded)
+ spin_unlock_irqrestore(&port->lock, flags);
+ else
+ spin_unlock(&port->lock);
+
tty_flip_buffer_push(tport);
- spin_lock(&port->lock);
}

static void stm32_usart_tx_dma_complete(void *arg)
@@ -458,8 +466,6 @@ static irqreturn_t stm32_usart_interrupt(int irq, void *ptr)
const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
u32 sr;

- spin_lock(&port->lock);
-
sr = readl_relaxed(port->membase + ofs->isr);

if ((sr & USART_SR_RTOF) && ofs->icr != UNDEF_REG)
@@ -473,10 +479,11 @@ static irqreturn_t stm32_usart_interrupt(int irq, void *ptr)
if ((sr & USART_SR_RXNE) && !(stm32_port->rx_ch))
stm32_usart_receive_chars(port, false);

- if ((sr & USART_SR_TXE) && !(stm32_port->tx_ch))
+ if ((sr & USART_SR_TXE) && !(stm32_port->tx_ch)) {
+ spin_lock(&port->lock);
stm32_usart_transmit_chars(port);
-
- spin_unlock(&port->lock);
+ spin_unlock(&port->lock);
+ }

if (stm32_port->rx_ch)
return IRQ_WAKE_THREAD;
@@ -489,13 +496,9 @@ static irqreturn_t stm32_usart_threaded_interrupt(int irq, void *ptr)
struct uart_port *port = ptr;
struct stm32_port *stm32_port = to_stm32_port(port);

- spin_lock(&port->lock);
-
if (stm32_port->rx_ch)
stm32_usart_receive_chars(port, true);

- spin_unlock(&port->lock);
-
return IRQ_HANDLED;
}

--
2.30.2