linux-kernel - Re: [RT] Lockdep warning on boot with 2.6.31-rc5-rt1.1

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 7 Aug 2009 17:30:45 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Clark Williams <williams@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	RT <linux-rt-users@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"greg@...ah.com" <greg@...ah.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Kay Sievers <kay.sievers@...y.org>
Subject: Re: [RT] Lockdep warning on boot with 2.6.31-rc5-rt1.1

On Fri, 7 Aug 2009, Peter Zijlstra wrote:

> On Fri, 2009-08-07 at 12:45 -0400, Alan Stern wrote:
> > On Fri, 7 Aug 2009, Peter Zijlstra wrote:
> 
> > > The other proposal was creating a fixed list of classes and register
> > > each device at a class corresponding to its depth in the tree. I can't
> > > remember what was wrong with that, but I seem to have been persuaded
> > > that that was hard too.
> > 
> > It probably would work for the most part.  However a possible scenario
> > involves first locking a parent and then locking all its children.  (I
> > don't know if this ever happens anywhere, but it might.)  This can't
> > cause a deadlock but it would run into trouble with depth-based
> > classes.
> 
> If you know which parent is locked, we can solve that with
> mutex_lock_nest_lock() [ doesn't currently exist, but is analogous to
> spin_lock_nest_lock() ] and together with
> http://lkml.org/lkml/2009/7/23/222 that would allow you to lock up to
> 2048 children.

Not only do I know not which parent is locked, I don't even know if 
this ever happens anywhere at all!  My point was purely theoretical.

> Would something like that work?

Perhaps -- I don't understand what spin_lock_nest_lock() is supposed to
do.

Alan Stern

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/