Hi,
On Wed, Nov 27, 2019 at 10:16 PM Leo Yan <leo.yan@xxxxxxxxxx> wrote:
>
> As the commit 677fe555cbfb ("serial: imx: Fix recursive locking bug")
> has mentioned the uart driver might cause recursive locking between
> normal printing and the kernel debugging facilities (e.g. sysrq and
> oops). In the commit it gave out suggestion for fixing recursive
> locking issue: "The solution is to avoid locking in the sysrq case
> and trylock in the oops_in_progress case."
>
> This patch follows the suggestion (also used the exactly same code with
> other serial drivers, e.g. amba-pl011.c) to fix the recursive locking
> issue, this can avoid stuck caused by deadlock and print out log for
> sysrq and oops.
>
> Fixes: 04896a77a97b ("msm_serial: serial driver for MSM7K onboard serial peripheral.")
> Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>
> ---
> drivers/tty/serial/msm_serial.c | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c
> index 3657a24913fc..889538182e83 100644
> --- a/drivers/tty/serial/msm_serial.c
> +++ b/drivers/tty/serial/msm_serial.c
> @@ -1576,6 +1576,7 @@ static void __msm_console_write(struct uart_port *port, const char *s,
> int num_newlines = 0;
> bool replaced = false;
> void __iomem *tf;
> + int locked = 1;
>
> if (is_uartdm)
> tf = port->membase + UARTDM_TF;
> @@ -1588,7 +1589,13 @@ static void __msm_console_write(struct uart_port *port, const char *s,
> num_newlines++;
> count += num_newlines;
>
> - spin_lock(&port->lock);
> + if (port->sysrq)
> + locked = 0;
> + else if (oops_in_progress)
> + locked = spin_trylock(&port->lock);
> + else
> + spin_lock(&port->lock);
I don't have tons of experience with the "msm" serial driver, but the
above snippet tickled a memory in my brain for when I was looking at
the "qcom_geni" serial driver, which is a close cousin.
I seemed to remember that the "if (port->sysrq)" was something you
didn't want. ...but maybe that's only if you do something like commit
336447b3298c ("serial: qcom_geni_serial: Process sysrq at port unlock
time")? Any way you can try making a similar change to the msm driver
and see if it allow you to remove the special case for "port->sysrq"?
-Doug
