linux-kernel - Re: [PATCH 0/5] lockdep: (Was: check && lockdep_no

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Message-ID: <Pine.LNX.4.44L0.1401201328330.24630-100000@netrider.rowland.org>
Date:	Mon, 20 Jan 2014 13:37:53 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Oleg Nesterov <oleg@...hat.com>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: [PATCH 0/5] lockdep: (Was: check && lockdep_no_validate)

On Mon, 20 Jan 2014, Oleg Nesterov wrote:

> On 01/17, Alan Stern wrote:
> >
> > On Fri, 17 Jan 2014, Oleg Nesterov wrote:
> >
> > > Yes, sure. This change assumes that the only problem in drivers/base is
> > > dev->parent->mutex / dev->mutex dependency. If the locking is even more
> > > "broken" (wrt lockdep), we can't replace lockdep_set_novalidate_class()
> > > with lockdep_set_auto_nested().
> >
> > I suspect it is even more "broken".  But I can't point to specific
> > examples.
> >
> > ...
> >
> > My guess is that if your change is deployed widely, there will be
> > reports of violations.  That's only a guess.
> 
> OK, lets (try to) do this later. Let me send the changes which I hope
> should be fine in any case.
> 
> > Still, you could go ahead and try it, just to see what happens.
> 
> Yes, perhaps it makes sense at least to test this change and see what
> happens... We will see.
> 
> > Also, take a look at commit 356c05d58af0.  It's a similar situation
> > (not exactly the same).
> 
> At first glance, can't __ATTR_IGNORE_LOCKDEP() use no_validate too ?
> (ignoring the fact checkpatch.pl won't be happy). This can simplify
> the code, it seems.

Well, the macro itself doesn't specify the lockdep class.  That happens 
implicitly in sysfs_get_active(), in the call to rwsem_acquire_read().
However, it ought to be possible to change the code so that when 
ignore_lockdep(sd) returns nonzero, we end up using no_validate.

Alan Stern

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