Hello Jiri,
On Mon, 2023-03-06 at 10:43 +0100, Jiri Slaby wrote:
> On 06. 03. 23, 10:00, A. Sverdlin wrote:
> > From: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxxxx>
> >
> > From time to time DMA completion can come in the middle of DMA
> > shutdown:
> >
> > <process ctx>: <IRQ>:
> > lpuart32_shutdown()
> > lpuart_dma_shutdown()
> > del_timer_sync()
> > lpuart_dma_rx_complete()
> > lpuart_copy_rx_to_tty()
> > mod_timer()
> > lpuart_dma_rx_free()
> >
> > When the timer fires a bit later, sport->dma_rx_desc is NULL:
> >
> > Unable to handle kernel NULL pointer dereference at virtual address
> > 0000000000000004
> > pc : lpuart_copy_rx_to_tty+0xcc/0x5bc
> > lr : lpuart_timer_func+0x1c/0x2c
> > Call trace:
> > lpuart_copy_rx_to_tty
> > lpuart_timer_func
> > call_timer_fn
> > __run_timers.part.0
> > run_timer_softirq
> > __do_softirq
> > __irq_exit_rcu
> > irq_exit
> > handle_domain_irq
> > gic_handle_irq
> > call_on_irq_stack
> > do_interrupt_handler
> > ...
> >
> > To fix this fold del_timer_sync() into lpuart_dma_rx_free() after
> > dmaengine_terminate_sync() to make sure timer will not be re-
> > started in
> > lpuart_copy_rx_to_tty() <= lpuart_dma_rx_complete().
> >
> > Signed-off-by: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxxxx>
>
> This should have some Fixes: tag, I believe.
>
sure, you are right, I'll use
Fixes: 4a8588a1cf86 ("serial: fsl_lpuart: delete timer on shutdown")
on respin.
> > ---
> > drivers/tty/serial/fsl_lpuart.c | 11 +++--------
> > 1 file changed, 3 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/tty/serial/fsl_lpuart.c
> > b/drivers/tty/serial/fsl_lpuart.c
> > index e945f41b93d43..47c267ee22e04 100644
> > --- a/drivers/tty/serial/fsl_lpuart.c
> > +++ b/drivers/tty/serial/fsl_lpuart.c
> > @@ -1354,6 +1354,7 @@ static void lpuart_dma_rx_free(struct
> > uart_port *port)
> > struct dma_chan *chan = sport->dma_rx_chan;
> >
> > dmaengine_terminate_sync(chan);
>
> Maybe I'm missing something (I haven't looked into the code), but
> what
> happens if the timer ticks here? Won't the dmaengine be restarted
> there?
>
It's cyclic (used dmaengine_prep_dma_cyclic()), I see no restart in
lpuart_copy_rx_to_tty(), but maybe someone could double-check.
> > + del_timer_sync(&sport->lpuart_timer);
> > dma_unmap_sg(chan->device->dev, &sport->rx_sgl, 1,
> > DMA_FROM_DEVICE);
> > kfree(sport->rx_ring.buf);
> > sport->rx_ring.tail = 0;
>
>
--
Alexander Sverdlin
Siemens AG
www.siemens.com
