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serial: stm32: fix a deadlock condition with wakeup event 

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: 48a6092fb4 ("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>
pull/352/head
Erwan Le Ray 2021-03-04 17:23:00 +01:00 committed by Greg Kroah-Hartman
parent 25a8e7611d
commit ad76768124
1 changed files with 15 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

27
drivers/tty/serial/stm32-usart.c
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@ -214,13 +214,18 @@ 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;
@ -276,9 +281,12 @@ 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)
@ -459,8 +467,6 @@ 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)
@ -474,10 +480,11 @@ 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;
@ -490,13 +497,9 @@ 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;
}