On 2022-12-07 02:30:12 [+0100], Marek Vasut wrote:
> 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)
> }
> }
Why is this handler running as the primary handler to begin with?
There is
stm32_usart_rs485_rts_disable()
-> mctrl_gpio_set()
-> gpiod_set_array_value()
-> gpiod_set_array_value_complex()
-> gpio_chip_set_multiple()
-> gc->set_multiple() || gc->set() ?
-> bitmap_alloc() boom
I don't know if the underlying gpiod is always using a raw_spinlock_t
but that bitmap_alloc() (depending on FASTPATH_NGPIO()) is not going to
work.
pm_wakeup_dev_event() is also using a spinlock_t.
> - 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;
Before that, there is a "stm32_port->throttled" check using the very
same lock.
> if (stm32_usart_rx_dma_enabled(port))
> return IRQ_WAKE_THREAD;
Sebastian
