linux-kernel - Re: [PATCHv2-next 1/3] sysctl/sysrq: Remove __sysrq

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Date:   Wed, 15 Jan 2020 13:36:01 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Dmitry Safonov <dima@...sta.com>
Cc:     linux-kernel@...r.kernel.org,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Iurii Zaikin <yzaikin@...gle.com>,
        Jiri Slaby <jslaby@...e.com>, Joe Perches <joe@...ches.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Vasiliy Khoruzhick <vasilykh@...sta.com>,
        linux-serial@...r.kernel.org, Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCHv2-next 1/3] sysctl/sysrq: Remove __sysrq_enabled copy

On Tue, Jan 14, 2020 at 05:19:10PM +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@...gle.com>
> Cc: Jiri Slaby <jslaby@...e.com>
> Cc: Luis Chamberlain <mcgrof@...nel.org>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: linux-fsdevel@...r.kernel.org
> Signed-off-by: Dmitry Safonov <dima@...sta.com>
> ---
>  drivers/tty/sysrq.c   |  7 +++++++
>  include/linux/sysrq.h |  7 +++++++
>  kernel/sysctl.c       | 41 ++++++++++++++++++++++-------------------
>  3 files changed, 36 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;
> +}

Naming is hard.  And this name is really hard to understand.

Traditionally get/put are used for incrementing reference counts.  You
don't have a sysrq_put_mask() call, right?  :)

I think what you want this function to do is, "is sysrq enabled right
now" (hint, it's a global function, add kernel-doc to it so we know what
it does...).  If so, it should maybe be something like:

	bool sysrq_is_enabled(void);

which to me makes more sense.

thoughts?

thanks,

greg k-h