svn commit: r331298 - head/sys/dev/syscons

[Konstantin Belousov]

On Thu, Mar 22, 2018 at 04:53:22AM +1100, Bruce Evans wrote:
> Serial console drivers with fast interrupt handlers have much more
> broken locking for ddb special keys.  It is invalid to either drop locks
> or call the "any" function from a fast interrupt handler, but buggy
> serial console drivers calls kbd_alt_break(), and that now calls
> shutdown_nice() and other functions that cannot be called from a fast
> interrupt handler.  ddb keys supply most of the shutdown_nice()
> functionality for serial consoles, and there are no escape sequence to
> get this without ddb or maybe another debugger, so these bugs don't
> affect most users.
> 
> Handling this correctly requires much the same fix as an unsafe signal
> handler, and fixes have much the same problems -- not much more than
> setting a flag is safe, and the flag might never be looked at if the
> system is in a bad state.  However, if a nice shutdown is possible then
> the sytem must be in a good enough state to poll for flags.

Are you saying that fast interrupt handlers call shutdown_nice() ?  This
is the quite serious bug on its own.  To fix it, shutdown_nice() should
use a fast taskqueue to schedule the task which would lock the process
and send the signal.