Avoid locking in hard interrupt context, move the stm32_usart_transmit_chars() into the threaded IRQ handler. This fixes the following splat with preempt-rt: BUG: scheduling while atomic: (mount)/1289/0x00010001 Modules linked in: Preemption disabled at: [<c0119127>] irq_enter_rcu+0xb/0x42 CPU: 0 PID: 1289 Comm: (mount) Not tainted 6.1.0-rc7-rt5-stable-standard-00006-gd70aeccb9f0f #17 Hardware name: STM32 (Device Tree Support) unwind_backtrace from show_stack+0xb/0xc show_stack from dump_stack_lvl+0x2b/0x34 dump_stack_lvl from __schedule_bug+0x53/0x80 __schedule_bug from __schedule+0x47/0x404 __schedule from schedule_rtlock+0x15/0x34 schedule_rtlock from rtlock_slowlock_locked+0x1d7/0x57e rtlock_slowlock_locked from rt_spin_lock+0x29/0x3c rt_spin_lock from stm32_usart_interrupt+0xa9/0x110 stm32_usart_interrupt from __handle_irq_event_percpu+0x73/0x14e __handle_irq_event_percpu from handle_irq_event_percpu+0x9/0x22 handle_irq_event_percpu from handle_irq_event+0x53/0x76 handle_irq_event from handle_fasteoi_irq+0x65/0xa8 handle_fasteoi_irq from handle_irq_desc+0xf/0x18 handle_irq_desc from gic_handle_irq+0x45/0x54 gic_handle_irq from generic_handle_arch_irq+0x19/0x2c generic_handle_arch_irq from call_with_stack+0xd/0x10 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: Jean Philippe Romain <jean-philippe.romain@xxxxxxxxxxx> 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 --- drivers/tty/serial/stm32-usart.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-) diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c index a1490033aa164..56357a7962edc 100644 --- a/drivers/tty/serial/stm32-usart.c +++ b/drivers/tty/serial/stm32-usart.c @@ -791,11 +791,8 @@ static irqreturn_t stm32_usart_interrupt(int irq, void *ptr) } } - if ((sr & USART_SR_TXE) && !(stm32_port->tx_ch)) { - spin_lock(&port->lock); - stm32_usart_transmit_chars(port); - spin_unlock(&port->lock); - } + if ((sr & USART_SR_TXE) && !(stm32_port->tx_ch)) + return IRQ_WAKE_THREAD; if (stm32_usart_rx_dma_enabled(port)) return IRQ_WAKE_THREAD; @@ -808,8 +805,18 @@ 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; + const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs; unsigned long flags; + unsigned int size; + u32 sr; + + sr = readl_relaxed(port->membase + ofs->isr); + + if ((sr & USART_SR_TXE) && !(stm32_port->tx_ch)) { + spin_lock_irqsave(&port->lock, flags); + stm32_usart_transmit_chars(port); + spin_unlock_irqrestore(&port->lock, flags); + } /* Receiver timeout irq for DMA RX */ if (!stm32_port->throttled) { -- 2.35.1