Re: [PATCH 2/2] serial: earlycon: Make early_con as __initdata

Sergey Senozhatsky
2017-07-07T04:47:12Z

On (07/06/17 11:38), Matt Redfearn wrote:
> All early console drivers that may be registered as the earlycon are
> marked __init to be placed in the init section. The drivers' code and
> data are freed during free_initmem_default() but the early console is
> not unregistered in printk_late_init() as the init_section_intersects()
> test fails. This leads to the earlycon still being active, potentially
> with dangling pointers into the freed init section, which may have been
> poisoned by the slab debugger. Attempting to use the boot console after
> this will likely lead to weird behaviour and kernel crashes.

people want to use early-con as a panic() console fallback.

-ss

> Fix this by marking the early_con struct __initdata so that the
> init_section_intersects() test succeeds and the console is unregistered
> in printk_late_init() before the init section is freed.
>
> The 8250 earlycon, on which the generic earlycon was based, had these
> attributes on it's console struct. The switch to the generic
> implementation in commit d2fd6810a823 ("tty/serial: convert 8250 to
> generic earlycon") appears to have broken unregistraton of the boot
> console when its code and data are in __init.
>
> Fixes: d2fd6810a823 ("tty/serial: convert 8250 to generic earlycon")
> Signed-off-by: Matt Redfearn <matt.redfearn@imgtec.com>
>
> ---
>
> drivers/tty/serial/earlycon.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/tty/serial/earlycon.c b/drivers/tty/serial/earlycon.c
> index c3651540e1ba..388aaafcca2b 100644
> --- a/drivers/tty/serial/earlycon.c
> +++ b/drivers/tty/serial/earlycon.c
> @@ -29,13 +29,13 @@
>
> #include <asm/serial.h>
>
> -static struct console early_con = {
> +static struct console early_con __initdata = {
> .name = "uart", /* fixed up at earlycon registration */
> .flags = CON_PRINTBUFFER | CON_BOOT,
> .index = 0,
> };
>
> -static struct earlycon_device early_console_dev = {
> +static struct earlycon_device early_console_dev __initdata = {
> .con = &early_con,
> };
>
> --
> 2.7.4
>