On Fri, Dec 16, 2022 at 12:53:38PM +0100, Marek Vasut wrote:
> Requesting an interrupt with IRQF_ONESHOT will run the primary handler
> in the hard-IRQ context even in the force-threaded mode. The
> force-threaded mode is used by PREEMPT_RT in order to avoid acquiring
> sleeping locks (spinlock_t) in hard-IRQ context. This combination
> makes it impossible and leads to "sleeping while atomic" warnings.
>
> Use one interrupt handler for both handlers (primary and secondary)
> and drop the IRQF_ONESHOT flag which is not needed.
>
> Fixes: e359b4411c283 ("serial: stm32: fix threaded interrupt handling")
I don't think a Fixes tag is warranted as this is only needed due to
this undocumented quirk of PREEMPT_RT.
And this should not be backported in any case.
> Reviewed-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> Signed-off-by: Marek Vasut <marex@xxxxxxx>
> ---
> Cc: Alexandre Torgue <alexandre.torgue@xxxxxxxxxxx>
> Cc: Erwan Le Ray <erwan.leray@xxxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Jiri Slaby <jirislaby@xxxxxxxxxx>
> Cc: Maxime Coquelin <mcoquelin.stm32@xxxxxxxxx>
> Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Valentin Caron <valentin.caron@xxxxxxxxxxx>
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Cc: linux-stm32@xxxxxxxxxxxxxxxxxxxxxxxxxxxx
> To: linux-serial@xxxxxxxxxxxxxxx
> ---
> V2: - Update patch subject, was:
> serial: stm32: Move hard IRQ handling to threaded interrupt context
> - Use request_irq() instead, rename the IRQ handler function
> V3: - Update the commit message per suggestion from Sebastian
> - Add RB from Sebastian
> - Add Fixes tag
> ---
> drivers/tty/serial/stm32-usart.c | 29 +++++++----------------------
> 1 file changed, 7 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
> index dfdbcf092facc..bbbab8dc2bfa9 100644
> --- a/drivers/tty/serial/stm32-usart.c
> +++ b/drivers/tty/serial/stm32-usart.c
> @@ -752,8 +752,9 @@ static irqreturn_t stm32_usart_interrupt(int irq, void *ptr)
> 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;
> - u32 sr;
> + unsigned long flags;
> unsigned int size;
> + u32 sr;
>
> sr = readl_relaxed(port->membase + ofs->isr);
>
> @@ -793,27 +794,13 @@ static irqreturn_t stm32_usart_interrupt(int irq, void *ptr)
> }
>
> if ((sr & USART_SR_TXE) && !(stm32_port->tx_ch)) {
> - spin_lock(&port->lock);
> + spin_lock_irqsave(&port->lock, flags);
> stm32_usart_transmit_chars(port);
> - spin_unlock(&port->lock);
> + spin_unlock_irqrestore(&port->lock, flags);
This is not needed as the handler runs with interrupts disabled.
> }
>
> - if (stm32_usart_rx_dma_enabled(port))
> - return IRQ_WAKE_THREAD;
> - else
> - return IRQ_HANDLED;
> -}
> -
> -static irqreturn_t stm32_usart_threaded_interrupt(int irq, void *ptr)
> -{
> - struct uart_port *port = ptr;
> - struct tty_port *tport = &port->state->port;
> - struct stm32_port *stm32_port = to_stm32_port(port);
> - unsigned int size;
> - unsigned long flags;
> -
> /* Receiver timeout irq for DMA RX */
> - if (!stm32_port->throttled) {
> + if (stm32_usart_rx_dma_enabled(port) && !stm32_port->throttled) {
> spin_lock_irqsave(&port->lock, flags);
But you could change this to spin_lock() now.
> size = stm32_usart_receive_chars(port, false);
> uart_unlock_and_check_sysrq_irqrestore(port, flags);
> @@ -1016,10 +1003,8 @@ static int stm32_usart_startup(struct uart_port *port)
> u32 val;
> int ret;
>
> - ret = request_threaded_irq(port->irq, stm32_usart_interrupt,
> - stm32_usart_threaded_interrupt,
> - IRQF_ONESHOT | IRQF_NO_SUSPEND,
> - name, port);
> + ret = request_irq(port->irq, stm32_usart_interrupt,
> + IRQF_NO_SUSPEND, name, port);
> if (ret)
> return ret;
You should also remove
/*
* Using DMA and threaded handler for the console could lead to
* deadlocks.
*/
if (uart_console(port))
return -ENODEV;
from stm32_usart_of_dma_rx_probe() when removing the threaded handler.
Johan
