Re: [RFC][PATCHv5 3/7] printk: introduce per-cpu safe_print seq buffer

Sergey Senozhatsky
2016-12-10T03:10:32Z

On (12/09/16 17:46), Petr Mladek wrote:
> > -/*
> > - * Safe printk() for NMI context. It uses a per-CPU buffer to
> > - * store the message. NMIs are not nested, so there is always only
> > - * one writer running. But the buffer might get flushed from another
> > - * CPU, so we need to be careful.
> > - */
>
> We should keep/create a good description here because the function
> has a non-trivial code. What about something like?
>

which is really not related to this patch set.

> > * Make sure that all old data have been read before the buffer was
> > @@ -261,14 +263,95 @@ void printk_safe_flush_on_panic(void)
> > printk_safe_flush();
> > }
> >
> > +#ifdef CONFIG_PRINTK_NMI
> > +/*
> > + * Safe printk() for NMI context. It uses a per-CPU buffer to
> > + * store the message. NMIs are not nested, so there is always only
> > + * one writer running. But the buffer might get flushed from another
> > + * CPU, so we need to be careful.
> > + */
>
> Hmm, I wanted to describe why we need another per-CPU buffer in NMI
> and I am not sure that we really need it.

NMI-printk can interrupt safe-printk's vsnprintf() in the middle of
the "while (*fmt)" loop: safe-priNMI-PRINTK

-ss