Hi, Geert,
On 27.11.2024 18:28, Geert Uytterhoeven wrote:
> Hi Claudiu,
>
> Thanks for your patch, which is now commit 3791ea69a4858b81 ("serial:
> sh-sci: Clean sci_ports[0] after at earlycon exit") in tty/tty-next.
>
> On Wed, Nov 6, 2024 at 1:02 PM Claudiu <claudiu.beznea@xxxxxxxxx> wrote:
>> From: Claudiu Beznea <claudiu.beznea.uj@xxxxxxxxxxxxxx>
>>
>> The early_console_setup() function initializes the sci_ports[0].port with
>> an object of type struct uart_port obtained from the object of type
>> struct earlycon_device received as argument by the early_console_setup().
>>
>> It may happen that later, when the rest of the serial ports are probed,
>> the serial port that was used as earlycon (e.g., port A) to be mapped to a
>> different position in sci_ports[] and the slot 0 to be used by a different
>> serial port (e.g., port B), as follows:
>>
>> sci_ports[0] = port A
>> sci_ports[X] = port B
>
> Haven't you mixed A and B?
>
>> In this case, the new port mapped at index zero will have associated data
>> that was used for earlycon.
>
> Oops, do you have a simple reproducer for this?
It is reproducible with patches:
- [PATCH 6/9] arm64: dts: renesas: rzg3s-smarc: Fix the debug serial alias
- [PATCH 9/9] arm64: dts: renesas: r9a08g045s33-smarc-pmod: Add overlay for
SCIF1
After boot, cat /dev/ttySC0 will lead to the issue described.
>
>> In case this happens, after Linux boot, any access to the serial port that
>> maps on sci_ports[0] (port A) will block the serial port that was used as
>> earlycon (port B).
>
> Again, A <-> B?
>
>> To fix this, add early_console_exit() that clean the sci_ports[0] at
>> earlycon exit time.
>>
>> Fixes: 0b0cced19ab1 ("serial: sh-sci: Add CONFIG_SERIAL_EARLYCON support")
>> Cc: stable@xxxxxxxxxxxxxxx
>> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@xxxxxxxxxxxxxx>
>
> This causes a crash (lock-up without any output) when
> CONFIG_DEBUG_SPINLOCK=y (e.g. CONFIG_PROVE_LOCKING=y).
I missed to check this. Thank you for testing it.
>
>> --- a/drivers/tty/serial/sh-sci.c
>> +++ b/drivers/tty/serial/sh-sci.c
>> @@ -3546,6 +3546,32 @@ sh_early_platform_init_buffer("earlyprintk", &sci_driver,
>> #ifdef CONFIG_SERIAL_SH_SCI_EARLYCON
>> static struct plat_sci_port port_cfg __initdata;
>>
>> +static int early_console_exit(struct console *co)
>> +{
>> + struct sci_port *sci_port = &sci_ports[0];
>> + struct uart_port *port = &sci_port->port;
>> + unsigned long flags;
>> + int locked = 1;
>> +
>> + if (port->sysrq)
>> + locked = 0;
>> + else if (oops_in_progress)
>> + locked = uart_port_trylock_irqsave(port, &flags);
>> + else
>> + uart_port_lock_irqsave(port, &flags);
>> +
>> + /*
>> + * Clean the slot used by earlycon. A new SCI device might
>> + * map to this slot.
>> + */
>> + memset(sci_ports, 0, sizeof(*sci_port));
>
> Nit: I'd rather use "*sci_port" instead of "sci_ports".
That would be better, indeed.
>
>> +
>> + if (locked)
>> + uart_port_unlock_irqrestore(port, flags);
>
> "BUG: spinlock bad magic", as you've just cleared the port, including
> the spinlock.
>
> I guess we can just remove all locking from this function to fix this?
I'll look to it.
>
> However, could it happen that the new device taking slot 0 is probed
> before the early console is terminated?
I don't know to answer this. In my testing I haven't encountered it.
> In that case, its active
> sci_ports[] entry would be cleared when early_console_exit() is called.
>
> Also, what happens if "earlycon keep_bootcon" is passed on the kernel
> command line, and the new device takes slot 0?
I checked it with earlycon and the serial device being on slot 0. In this
case it was OK.
>
> Thanks!
>
>> +
>> + return 0;
>> +}
>> +
>> static int __init early_console_setup(struct earlycon_device *device,
>> int type)
>> {
>> @@ -3562,6 +3588,8 @@ static int __init early_console_setup(struct earlycon_device *device,
>> SCSCR_RE | SCSCR_TE | port_cfg.scscr);
>>
>> device->con->write = serial_console_write;
>> + device->con->exit = early_console_exit;
>> +
>> return 0;
>> }
>> static int __init sci_early_console_setup(struct earlycon_device *device,
>
> Gr{oetje,eeting}s,
>
> Geert
>
