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    Subject[PATCH 5.10 135/530] serial: stm32: fix a deadlock condition with wakeup event
    Date
    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


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