Re: [PATCH] tty: serial: amba-pl011: cancel RS485 trigger hrtimers before removal

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Jul 21, 2026 at 04:28:58AM +0000, Fan Wu wrote:
> pl011_shutdown() calls pl011_rs485_tx_stop() when RS485 is enabled and
> the transmit state machine is still active.  That function may re-arm
> the trigger_stop_tx hrtimer via hrtimer_start() when the TX FIFO is not
> yet empty, or when delay_rts_after_send is configured, and the trigger
> timers can equally be left armed from a prior pl011_rs485_tx_start().
> 
> On removal, uart_remove_one_port() can finish without draining the RS485
> hrtimers, and devm frees the uart_amba_port once pl011_remove() returns.
> The existing teardown syncs do not help here: pl011_disable_interrupts()
> only masks the UART IMSC register, pl011_dma_shutdown() cancels a
> different (DMA rx) timer_list, and free_irq() plus serial_core's
> synchronize_irq() only drain the UART interrupt handler, not the hrtimer
> softirq callbacks.  Either trigger callback can therefore recover uap
> from its embedded hrtimer and access uap->port after the free.
> 
> Cancel both RS485 trigger hrtimers in pl011_shutdown(), after the
> re-arming pl011_rs485_tx_stop() call and before free_irq(), and again
> in pl011_remove() after uart_remove_one_port().  The remove-side
> calls cover paths such as suspend followed by unbind, where serial
> core need not invoke the driver's shutdown callback.  The
> callbacks pl011_trigger_start_tx and pl011_trigger_stop_tx return
> HRTIMER_NORESTART, so hrtimer_cancel() fully drains any pending and
> concurrently running callback without a self-restart loop.  As
> pl011_trigger_start_tx() may re-enable the TX interrupt via
> pl011_start_tx(), call pl011_disable_interrupts() again after the
> cancels to re-mask IMSC before free_irq().  The cancel site does not
> hold uart_port_lock across the cancel
> (pl011_disable_interrupts() already released it) and the callbacks take
> that lock internally, so there is no self-deadlock.  This mirrors the
> RS485 teardown pattern in 8250_port.c (serial8250_em485_destroy),
> which cancels both hrtimers before the embedding object is freed.
> 
> This issue was found by an in-house static analysis tool.

Yes, but a LLM obviously wrote the text here.  Please shorten it up a
LOT and make it more concise, as-is, it's impossible to read this
wall-of-text...

thanks,

greg k-h