Re: [PATCH v4 1/2] tty: sysrq: don't expose a partially written reset_seq

[Greg KH <gregkh@linuxfoundation.org>]

On Fri, Oct 30, 2026 at 02:30:53PM +0800, Zhan Xusheng wrote:
> Hi Greg,
> 
> On Fri, Oct 30, 2026 at 07:05:10AM +0100, Greg KH wrote:
> > I'm sorry, but I can't really parse this llm-generated text.  What is
> > the bug here.  What is being fixed?  And what is changing?
> 
> Sorry, that was unreadable.
> 
> reset_seq can be changed at runtime, but the new value doesn't work:
> each keyboard keeps counting the old keys too, so pressing the new
> sequence does nothing.  2/2 fixes that.

So the new value never worked?  This feature does not work?

> 1/2 is for a race that 2/2 makes easier to hit.  The new list is filled
> in one key at a time and the keyboards pick up each partial list, so
> pressing the first new key during the write can reboot the machine.

So the issue is that changing the sequence can race with what exactly?

> > And how has no one ever hit this issue in the decades that it has been
> > present?  Is this really something that needs to be fixed?  If so, why?
> 
> The sequence is usually set on the command line or in DT, and that
> works.  Both bugs need a runtime change, and the race also needs a key
> press during the write, which takes microseconds.  I only hit it with
> an added delay.

What race exactly?  That when this is being changed "something happens"?

> 1/2 is far too big for that.  Telling the keyboards about the new value
> only once the whole list is written avoids the race with a small patch,
> and doesn't change what the parameter accepts.  I can send that with
> 2/2 as v5, or drop the series if runtime changes aren't worth fixing.

I still don't understand what the root problem is here, sorry.

thanks,

greg k-h