On Thu, Jan 09, 2020 at 09:54:43PM +0000, Dmitry Safonov wrote:
> Many embedded boards have a disconnected TTL level serial which can
> generate some garbage that can lead to spurious false sysrq detects.
>
> Currently, sysrq can be either completely disabled for serial console
> or always disabled (with CONFIG_MAGIC_SYSRQ_SERIAL), since
> commit 732dbf3a6104 ("serial: do not accept sysrq characters via serial port")
>
> At Arista, we have such boards that can generate BREAK and random
> garbage. While disabling sysrq for serial console would solve
> the problem with spurious false sysrq triggers, it's also desirable
> to have a way to enable sysrq back.
>
> Having the way to enable sysrq was beneficial to debug lockups with
> a manual investigation in field and on the other side preventing false
> sysrq detections.
>
> As a preparation to add sysrq_toggle_support() call into uart,
> remove a private copy of sysrq_enabled from sysctl - it should reflect
> the actual status of sysrq.
>
> Furthermore, the private copy isn't correct already in case
> sysrq_always_enabled is true. So, remove __sysrq_enabled and use a
> getter-helper for sysrq enabled status.
>
> Cc: Iurii Zaikin <yzaikin@xxxxxxxxxx>
> Cc: Jiri Slaby <jslaby@xxxxxxxx>
> Cc: Luis Chamberlain <mcgrof@xxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx
> Signed-off-by: Dmitry Safonov <dima@xxxxxxxxxx>
> ---
> drivers/tty/sysrq.c | 7 +++++++
> include/linux/sysrq.h | 1 +
> kernel/sysctl.c | 41 ++++++++++++++++++++++-------------------
> 3 files changed, 30 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
> index f724962a5906..ef3e78967146 100644
> --- a/drivers/tty/sysrq.c
> +++ b/drivers/tty/sysrq.c
> @@ -73,6 +73,13 @@ static bool sysrq_on_mask(int mask)
> (sysrq_enabled & mask);
> }
>
> +int sysrq_get_mask(void)
> +{
> + if (sysrq_always_enabled)
> + return 1;
> + return sysrq_enabled;
> +}
> +
> static int __init sysrq_always_enabled_setup(char *str)
> {
> sysrq_always_enabled = true;
> diff --git a/include/linux/sysrq.h b/include/linux/sysrq.h
> index 8c71874e8485..4a0b351fa2d3 100644
> --- a/include/linux/sysrq.h
> +++ b/include/linux/sysrq.h
> @@ -50,6 +50,7 @@ int unregister_sysrq_key(int key, struct sysrq_key_op *op);
> struct sysrq_key_op *__sysrq_get_key_op(int key);
>
> int sysrq_toggle_support(int enable_mask);
> +int sysrq_get_mask(void);
>
> #else
>
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index d396aaaf19a3..6ddb4d7df0e1 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -229,25 +229,8 @@ static int proc_dopipe_max_size(struct ctl_table *table, int write,
> void __user *buffer, size_t *lenp, loff_t *ppos);
>
> #ifdef CONFIG_MAGIC_SYSRQ
> -/* Note: sysrq code uses its own private copy */
> -static int __sysrq_enabled = CONFIG_MAGIC_SYSRQ_DEFAULT_ENABLE;
> -
> static int sysrq_sysctl_handler(struct ctl_table *table, int write,
> - void __user *buffer, size_t *lenp,
> - loff_t *ppos)
> -{
> - int error;
> -
> - error = proc_dointvec(table, write, buffer, lenp, ppos);
> - if (error)
> - return error;
> -
> - if (write)
> - sysrq_toggle_support(__sysrq_enabled);
> -
> - return 0;
> -}
> -
> + void __user *buffer, size_t *lenp, loff_t *ppos);
> #endif
>
> static struct ctl_table kern_table[];
> @@ -747,7 +730,7 @@ static struct ctl_table kern_table[] = {
> #ifdef CONFIG_MAGIC_SYSRQ
> {
> .procname = "sysrq",
> - .data = &__sysrq_enabled,
> + .data = NULL,
> .maxlen = sizeof (int),
> .mode = 0644,
> .proc_handler = sysrq_sysctl_handler,
> @@ -2844,6 +2827,26 @@ static int proc_dostring_coredump(struct ctl_table *table, int write,
> }
> #endif
>
> +#ifdef CONFIG_MAGIC_SYSRQ
> +static int sysrq_sysctl_handler(struct ctl_table *table, int write,
> + void __user *buffer, size_t *lenp, loff_t *ppos)
> +{
> + int tmp, ret;
> +
> + tmp = sysrq_get_mask();
> +
> + ret = __do_proc_dointvec(&tmp, table, write, buffer,
> + lenp, ppos, NULL, NULL);
> + if (ret || !write)
> + return ret;
> +
> + if (write)
> + sysrq_toggle_support(tmp);
> +
> + return 0;
> +}
> +#endif
Why did you move this function down here? Can't it stay where it is and
you can just fix the logic there? Now you have two different #ifdef
blocks intead of just one :(
thanks,
greg k-h
