linux-kernel - Re: [PATCH 2/2] lockdep: choose to continue lock debugging despite taint

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Date:	Sat, 11 Apr 2009 03:37:54 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Greg KH <gregkh@...e.de>, LKML <linux-kernel@...r.kernel.org>,
	LTP <ltp-list@...ts.sourceforge.net>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 2/2] lockdep: choose to continue lock debugging despite
	taint

On Sat, Apr 11, 2009 at 03:15:06AM +0200, Frederic Weisbecker wrote:
> On Fri, Apr 10, 2009 at 03:45:20PM +0200, Ingo Molnar wrote:
> > 
> > * Frederic Weisbecker <fweisbec@...il.com> wrote:
> > 
> > > On Fri, Apr 10, 2009 at 02:15:15PM +0200, Ingo Molnar wrote:
> > > > 
> > > > * Frederic Weisbecker <fweisbec@...il.com> wrote:
> > > > 
> > > > > Lockdep is disabled after any kernel taints. This might be 
> > > > > convenient to ignore bad locking issues which sources come from 
> > > > > outside the kernel tree. Nevertheless, it might be a frustrating 
> > > > > experience for the staging developers or anyone who might develop 
> > > > > a kernel that happens to be tainted.
> > > > 
> > > > Good point. Not having lockdep coverage for drivers/staging/ just 
> > > > prolongs their transition - not good.
> > > > 
> > > > But instead of this:
> > > > 
> > > > >  void add_taint(unsigned flag)
> > > > >  {
> > > > > +#ifndef CONFIG_LOCKDEP_IGNORE_TAINT
> > > > >  	/*
> > > > >  	 * Can't trust the integrity of the kernel anymore.
> > > > >  	 * We don't call directly debug_locks_off() because the issue
> > > > > @@ -220,6 +221,7 @@ void add_taint(unsigned flag)
> > > > >  	 */
> > > > >  	if (xchg(&debug_locks, 0))
> > > > >  		printk(KERN_WARNING "Disabling lockdep due to kernel taint\n");
> > > > > +#endif
> > > > 
> > > > I'd suggest to not do the debug_locks_off() call if TAINT_CRAP. I.e. 
> > > > something like:
> > > > 
> > > > 	if (!(flag & TAINT_CRAP) && debug_locks_off())
> > > > 		printk(...);
> > > > 
> > > > will do the trick.
> > > > 
> > > > 	Ingo
> > > 
> > > 
> > > Ok, but this is not only about staging. It's also about 
> > > TAINT_WARN. Just imagine that you report a warning to a 
> > > maintainer, and while you are waiting for it to be fixed, you 
> > > can't use lockdep for your own needs.
> > > 
> > > Hm?
> > 
> > We can exclude TAINT_WARN too - i.e. (TAINT_CRAP|TAINT_WARN).
> > 
> > 	Ingo
> 
> 
> Fine :-)
> 
> See the v2 on further mails in this thread.
> 
> Side request: do you think you could merge them on kill-the-BKL tree?


Sorry, forget about this side request. I thought merging tip:master
into tip:core/kill-the-BKL would make me suffer a rain of conflicts
but actually I've just tried and I only encountered a very simple
conflict in sched.c so it's very easy to manage it locally. Then
we can keep the history of kill-the-BKL, for now it's good as is.

Frederic.


> Thanks!
> 

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