Re: [PATCH V2] tty: serial: kgdboc: Fix 8250_* kgd over serial

[Doug Anderson]

Hi,

On Sun, Dec 17, 2023 at 11:34 PM Michael Trimarchi
<michael@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> Check if port type is not PORT_UNKNOWN during poll_init.
> The kgdboc calls the tty_find_polling_driver that check
> if the serial is able to use poll_init. The poll_init calls
> the uart uart_poll_init that try to configure the uart with the
> selected boot parameters. The uart must be ready before setting
> parameters. Seems that PORT_UNKNOWN is already used by other
> functions in serial_core to detect uart status, so use the same
> to avoid to use it in invalid state.
>
> The crash happen for instance in am62x architecture where the 8250
> register the platform driver after the 8250 core is initialized.
>
> Follow the report crash coming from KGDB
>
> Thread 2 received signal SIGSEGV, Segmentation fault.
> [Switching to Thread 1]
> _outb (addr=<optimized out>, value=<optimized out>) at ./include/asm-generic/io.h:584
> 584             __raw_writeb(value, PCI_IOBASE + addr);
> (gdb) bt
>
> This section of the code is too early because in this case
> the omap serial is not probed
>
> Thread 2 received signal SIGSEGV, Segmentation fault.
> [Switching to Thread 1]
> _outb (addr=<optimized out>, value=<optimized out>) at ./include/asm-generic/io.h:584
> 584             __raw_writeb(value, PCI_IOBASE + addr);
> (gdb) bt
>
> Thread 2 received signal SIGSEGV, Segmentation fault.
> [Switching to Thread 1]
> _outb (addr=<optimized out>, value=<optimized out>) at ./include/asm-generic/io.h:584
> 584             __raw_writeb(value, PCI_IOBASE + addr);
> (gdb) bt
> 0  _outb (addr=<optimized out>, value=<optimized out>) at ./include/asm-generic/io.h:584
> 1  logic_outb (value=0 '\000', addr=18446739675637874689) at lib/logic_pio.c:299
> 2  0xffff80008082dfcc in io_serial_out (p=0x0, offset=16760830, value=0) at drivers/tty/serial/8250/8250_port.c:416
> 3  0xffff80008082fe34 in serial_port_out (value=<optimized out>, offset=<optimized out>, up=<optimized out>)
>     at ./include/linux/serial_core.h:677
> 4  serial8250_do_set_termios (port=0xffff8000828ee940 <serial8250_ports+1568>, termios=0xffff80008292b93c, old=0x0)
>     at drivers/tty/serial/8250/8250_port.c:2860
> 5  0xffff800080830064 in serial8250_set_termios (port=0xfffffbfffe800000, termios=0xffbffe, old=0x0)
>     at drivers/tty/serial/8250/8250_port.c:2912
> 6  0xffff80008082571c in uart_set_options (port=0xffff8000828ee940 <serial8250_ports+1568>, co=0x0, baud=115200, parity=110, bits=8, flow=110)
>     at drivers/tty/serial/serial_core.c:2285
> 7  0xffff800080828434 in uart_poll_init (driver=0xfffffbfffe800000, line=16760830, options=0xffff8000828f7506 <config+6> "115200n8")
>     at drivers/tty/serial/serial_core.c:2656
> 8  0xffff800080801690 in tty_find_polling_driver (name=0xffff8000828f7500 <config> "ttyS2,115200n8", line=0xffff80008292ba90)
>     at drivers/tty/tty_io.c:410
> 9  0xffff80008086c0b0 in configure_kgdboc () at drivers/tty/serial/kgdboc.c:194
> 10 0xffff80008086c1ec in kgdboc_probe (pdev=0xfffffbfffe800000) at drivers/tty/serial/kgdboc.c:249
> 11 0xffff8000808b399c in platform_probe (_dev=0xffff000000ebb810) at drivers/base/platform.c:1404
> 12 0xffff8000808b0b44 in call_driver_probe (drv=<optimized out>, dev=<optimized out>) at drivers/base/dd.c:579
> 13 really_probe (dev=0xffff000000ebb810, drv=0xffff80008277f138 <kgdboc_platform_driver+48>) at drivers/base/dd.c:658
> 14 0xffff8000808b0d2c in __driver_probe_device (drv=0xffff80008277f138 <kgdboc_platform_driver+48>, dev=0xffff000000ebb810)
>     at drivers/base/dd.c:800
> 15 0xffff8000808b0eb8 in driver_probe_device (drv=0xfffffbfffe800000, dev=0xffff000000ebb810) at drivers/base/dd.c:830
> 16 0xffff8000808b0ff4 in __device_attach_driver (drv=0xffff80008277f138 <kgdboc_platform_driver+48>, _data=0xffff80008292bc48)
>     at drivers/base/dd.c:958
> 17 0xffff8000808ae970 in bus_for_each_drv (bus=0xfffffbfffe800000, start=0x0, data=0xffff80008292bc48,
>     fn=0xffff8000808b0f3c <__device_attach_driver>) at drivers/base/bus.c:457
> 18 0xffff8000808b1408 in __device_attach (dev=0xffff000000ebb810, allow_async=true) at drivers/base/dd.c:1030
> 19 0xffff8000808b16d8 in device_initial_probe (dev=0xfffffbfffe800000) at drivers/base/dd.c:1079
> 20 0xffff8000808af9f4 in bus_probe_device (dev=0xffff000000ebb810) at drivers/base/bus.c:532
> 21 0xffff8000808ac77c in device_add (dev=0xfffffbfffe800000) at drivers/base/core.c:3625
> 22 0xffff8000808b3428 in platform_device_add (pdev=0xffff000000ebb800) at drivers/base/platform.c:716
> 23 0xffff800081b5dc0c in init_kgdboc () at drivers/tty/serial/kgdboc.c:292
> 24 0xffff800080014db0 in do_one_initcall (fn=0xffff800081b5dba4 <init_kgdboc>) at init/main.c:1236
> 25 0xffff800081b0114c in do_initcall_level (command_line=<optimized out>, level=<optimized out>) at init/main.c:1298
> 26 do_initcalls () at init/main.c:1314
> 27 do_basic_setup () at init/main.c:1333
> 28 kernel_init_freeable () at init/main.c:1551
> 29 0xffff8000810271ec in kernel_init (unused=0xfffffbfffe800000) at init/main.c:1441
> 30 0xffff800080015e80 in ret_from_fork () at arch/arm64/kernel/entry.S:857
>
> Signed-off-by: Michael Trimarchi <michael@xxxxxxxxxxxxxxxxxxxx>
> ---
> v1 -> v2:
>         - fix if condition during submission
>         - improve a bit the commit message
> RFC -> v1:
>         - refuse uart that has type PORT_UNKNOWN
>
> ---
>  drivers/tty/serial/serial_core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

I'm not a total expert on this code, but this seems reasonable to me.
One nit is ${SUBJECT} should probably be "kgdb over serial" instead of
"kgd over serial"

Reviewed-by: Douglas Anderson <dianders@xxxxxxxxxxxx>


> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index f1348a509552..9b7ed4aac77a 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -2633,7 +2633,7 @@ static int uart_poll_init(struct tty_driver *driver, int line, char *options)
>         mutex_lock(&tport->mutex);
>
>         port = uart_port_check(state);
> -       if (!port || !(port->ops->poll_get_char && port->ops->poll_put_char)) {
> +       if (!port || port->type == PORT_UNKNOWN || !(port->ops->poll_get_char && port->ops->poll_put_char)) {

Another slight nit is that the above line feels a little long,
clocking in at 110 columns. I know the 80 column limit isn't so firm
these days, but if it were me I'd split it across 2 lines.

-Doug