Re: [RFC][PATCH v8 1/2] printk: Make printk() completely async

Sergey Senozhatsky
2016-04-01T01:13:04Z

Hello Jan,

On (03/29/16 11:14), Jan Kara wrote:
> On Fri 25-03-16 00:43:22, Sergey Senozhatsky wrote:
> > @@ -1655,6 +1670,14 @@ asmlinkage int vprintk_emit(int facility, int level,
> > raw_spin_lock(&logbuf_lock);
> > logbuf_cpu = this_cpu;
> >
> > + /*
> > + * Set printing kthread sleep condition early, under the
> > + * logbuf_lock, so it (if RUNNING) will go to console_lock()
> > + * and spin on logbuf_lock.
> > + */
> > + if (!in_panic && printk_kthread && !need_flush_console)
> > + need_flush_console = true;
> > +
> > if (unlikely(recursion_bug)) {
> > static const char recursion_msg[] =
> > "BUG: recent printk recursion!";
>
> I like the cleaned up need_flush_console handling! Just a suggestion: It
> may be more logical to handle need_flush_console setting under logbuf_lock
> but after we actually store the message in the buffer, not before. Doesn't
> matter for correctness now but may be more future-proof.

I wanted to set it asap (when we know for sure that we will log_store()),
to have a bit more chances to avoid schedule() in printing thread. well,
that's just several log_store()-s, not a big deal, so I guess I can move
it to:

+ if (...)
+ need_flush_console = true;
logbuf_cpu = UINT_MAX;
raw_spin_unlock(&logbuf_lock);
lockdep_on();
local_irq_restore(flags);

-ss