Re: [PATCH] panic: fix incomplete panic log in panic()

Andrew Morton
2012-10-22T19:51:07Z

On Mon, 22 Oct 2012 22:54:54 +0800
Qing Z <njumical@gmail.com> wrote:

> Hi Andrew,
> Basically, console_unlock() should be called to make panic
> log printed. Call console_unlock() in panic have some risks when
> recurse in it(are there other bad cases?). The condition is very rare
> and the two issue cases I list always happen between console_lock()
> and console_unlock(). So I think we need to couple with
> console_lock(), but should avoid the case that panic happen in
> console_unlock(). I think it is a more modest and safe way. Please
> corect me if there is something wrong. Thanks!
>
> bool Is_in_console_unlock;
> void console_unlock(void)
> {
> ...
> + Is_in_console_unlock = ture;
> /* flush buffered message fragment immediately to console */
> console_cont_flush(text, sizeof(text));
> again:
> for (;;) {
> ....
> + Is_in_console_unlock = false;
> }
>
> void panic(const char *fmt, ...)
> {
> ....
> + /*
> + * we should unlock console here to make oops log printed, in case
> + * console is locked before panic in this cpu, or other cpus lock the
> + * console before be stopped.
> + */
> + if( unlikely(console_locked) && !Is_in_console_unlock )
> + {
> + console_unlock();
> + console_locked = 0;
> + }
>
> /*
> * Note smp_send_stop is the usual smp shutdown function, which
> * unfortunately means it may not be hardened to work in a panic
> * situation.
> */
> smp_send_stop();
>
> ....
> }

Well, if something like that will solve the problem then yes, I guess
that is the way to go. It's not pretty, but it is clear and direct,
and this isn't a pretty problem!

But is this approach sufficient? What happens in the case of an oops
or a BUG() inside console_lock()?