Re: [PATCH 5/5] ring-buffer: fix printk output

[Andrew Morton]

On Wed, 29 Apr 2009 09:22:08 +0200 Ingo Molnar <mingo@xxxxxxx> wrote:

> 
> * Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> 
> > On Wed, 29 Apr 2009 08:09:55 +0200 Ingo Molnar <mingo@xxxxxxx> wrote:
> > 
> > > 
> > > * Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> > > 
> > > > On Wed, 29 Apr 2009 07:43:59 +0200 Ingo Molnar <mingo@xxxxxxx> wrote:
> > > > 
> > > > > 
> > > > > * Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> > > > > 
> > > > > > On Wed, 29 Apr 2009 00:48:19 -0400 Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> > > > > > 
> > > > > > > -	printk_once(KERN_WARNING "Tracing recursion: depth[%d]:"
> > > > > > > +	printk_once(KERN_WARNING "Tracing recursion: depth[%ld]:"
> > > > > > 
> > > > > > hrmph.  I didn't know that printk_once() existed, and I should 
> > > > > > have known.  I wonder how many other people don't know.
> > > > > 
> > > > > Was posted to linux-next@xxxxxxxxxxxxxxxx
> > > > 
> > > > Well no wonder I didn't know about it.
> > > 
> > > I (too?) think it's counter-productive that the linux-next list is 
> > > split out of lkml. I constantly fall into that trap: i get a 
> > > bugreport against one of our trees, i see that there's vger in the 
> > > Cc: list and mistake it for being Cc:-ed to lkml (all our trees are 
> > > developed on lkml and most of the bugreports come Cc:-ed to lkml) 
> > > but in reality it's Cc:-ed to linux-next which has a much smaller 
> > > audience. (which audience apparently does not even include you)
> > > 
> > > If this email list fragmentation and the resoluting loss of 
> > > information bothers you too then please ask Stephen to move 
> > > linux-next mails to lkml (i've Cc:-ed Stephen) - it's not like it's 
> > > actually something separate ... today's linux-next messages are 
> > > tomorrow's lkml messages. Moving linux-next mails to lkml would 
> > > nicely improve the S/N ratio on lkml.
> > > 
> > 
> > eh.  Just auto-add lkml to tipbot-commit emails?
> 
> Yeah - the tip-commits-bot already has such a feature and we are 
> making use of it - but this commit predates it. So it was posted to 
> linux-next and the tip-commits list.

there's a tip-commits list?

> My larger point remains, about possibly embedding linux-next into 
> lkml. I couldnt think of a single linux-next mail that isnt relevant 
> to lkml. It's all about commits that are destined for upstream in 
> 0-2.5 months.

Sure, I'd be OK with zapping the linux-next list.

> > printk_once() is racy on smp and preempt btw ;)
> 
> Like WARN_ONCE() and WARN_ON_ONCE(). It's really an "oh crap" 
> facility, not for normal kernel messages.
> 
> Do we want to complicate them with locking and preemption - or 
> should we just concentrate on getting the "oh crap" message out to 
> the syslog (before it's possibly too late to get anything out)?
> 
> I have no strong opinion about it - but i tend to like the simpler 
> method most. printk + stack dumps themselves arent atomic to begin 
> with.

Well, it's hardly likely to be a problem.  otoh, if two CPUs _do_ hit
the thing at the same time, the resulting output will be all messed up
and we'd really like to see it.

Easily fixed with test_and_set_bit()?
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