linux-kernel - Re: [PATCH] scheduler: fix x86 regression in native_sched

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Date:	Wed, 12 Dec 2007 11:44:41 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Stefano Brivio <stefano.brivio@...imi.it>,
	Robert Love <rml@...h9.net>, linux-kernel@...r.kernel.org,
	Dave Jones <davej@...hat.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Michael Buesch <mb@...sch.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Len Brown <lenb@...nel.org>
Subject: Re: [PATCH] scheduler: fix x86 regression in native_sched_clock


* Nick Piggin <nickpiggin@...oo.com.au> wrote:

> > the scariest bit is the adding of cpu_clock() to kernel/printk.c so 
> > late in the game, and the anti-recursion code i did there. Maybe 
> > because this only affects CONFIG_PRINTK_TIME we could try it even 
> > for v2.6.24.
> 
> Printk recursion I guess shouldn't happen, but if there is a bug 
> somewhere in eg. the scheduler locking, then it may trigger, right?

or we just crash somewhere. It's all about risk management - printk is 
crutial, and with more complex codepaths being touched in printk it 
might make sense to just add built-in recursion protection into printk 
via my patch.

> Probably pretty rare case, however it would be nice to be able to find 
> out where the recursion comes from? Can you put an instruction pointer 
> in the recursion message perhaps?

yeah, as i mentioned if this would be occuring in practice we can always 
save the stacktrace of the incident and output that. I opted for the 
simplest approach first. Thanks for your Reviewed-by, i've queued it up 
for 2.6.25.

	Ingo
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