Re: early_printk accessing __log_buf

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 23 Jul 2007 16:54:36 -0400
"Mike Frysinger" <vapier.adi@gmail.com> wrote:

> On 7/23/07, Andrew Morton <akpm@linux-foundation.org> wrote:
> > On Mon, 23 Jul 2007 14:19:12 -0400
> > Robin Getz <rgetz@blackfin.uclinux.org> wrote:
> >
> > > On Sun 22 Jul 2007 19:50, Mike Frysinger pondered:
> > > >
> > > > i think the attached two functions account for what Robin and Andrew
> > > > were thinking ...
> > >
> > > A note about why/when grab_lock would be set to zero (pre-kernel init, or
> > > OOPs) might be nice.
> >
> > Definitely.
> >
> > The pre-kernel init shouldn't be an issue: logbuf_lock is initialised at
> > compile time.
> >
> > At oops time we could possibly use oops_in_progress to work out whether to
> > avoid taking the lock.  That's not terribly nice, but nor is it nice for
> > callers to know about printk internals.
> 
> maybe, but for early debug users (the reason we wanted this
> originally), it wouldnt be an oops in progress ... but i guess we can
> just as easily set oops_in_progress to 1 in our code before calling
> this function to keep from having to worry over locks from being
> doubly grabbed.

I don't immediately see how logbuf_lock could be doubly grabbed.  Only if
you're calling this from hard irq context?