On Mon, 16 Oct 2017 22:13:05 +0900
Sergey Senozhatsky <sergey.senozhat...@gmail.com> wrote:
> just "brainstorming" it... with some silly ideas.
>
> pushing the data from NMI panic might look like we are replacing one
> deadlock scenario with another deadlock scenario. some of the console
> drivers are soooo complex internally. so I have been thinking about...
> may be we can extend struct console and add ->write_on_panic() and that
> handler must be as lockless as possible; so lockless that calling it
> from anything that is not panic() is a severe bug.
This may not be a bad idea. And make it so it can't be called unless we
are in panic mode (or at least "oops in progress").
If oops_in_progress is set, and the console has a "write_on_panic"
handler, then just call that.
Heck, if it doesn't have one, and early_printk is defined, then perhaps
that should be the default "write_on_panic" output?
-- Steve
>
> an absolutely trivial case,
> if serial console does
>
> console_write_cb(struct console *co, const char *s, unsigned int count)
> {
> spin_lock_irqsave(&port->lock, flags);
> uart_console_write(s, count, console_putchar);
> spin_unlock_irqrestore(&port->lock, flags);
> }
>
> then panic callback can look like
>
> console_write_on_panic_cb(struct console *co, const char *s, unsigned
> int count)
> {
> /* no, we don't take the port lock here */
> uart_console_write(s, count, console_putchar);
> }
>
> a less trivial case might look more involved. but in general that
> write_on_panic() callback must do the absolute minimum of work. so
> it's sort of a early console, but as part of normal console driver.
>
> I also got some other serial console crazy ideas, but they are not
> related to this topic.
>
> -ss
