linux-kernel - Re: dquot.c: possible circular locking Re: [2.6.20] BUG: workqueue leaked lock

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Date:	Tue, 20 Mar 2007 15:18:05 +0100
From:	Arjan van de Ven <arjan@...radead.org>
To:	Jan Kara <jack@...e.cz>
Cc:	Jarek Poplawski <jarkao2@...pl>,
	Folkert van Heusden <folkert@...heusden.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...sign.ru>,
	Neil Brown <neilb@...e.de>, Christoph Hellwig <hch@....de>
Subject: Re: dquot.c: possible circular locking Re: [2.6.20] BUG: workqueue
	leaked lock

On Tue, 2007-03-20 at 15:21 +0100, Jan Kara wrote:
> On Tue 20-03-07 14:35:10, Arjan van de Ven wrote:
> > 
> > 
> > >   Yes, I was looking at it. Hmm, we can possibly get rid of tty_mutex being
> > > acquired under dqptr_sem in quota code. But looking at the path from
> > > con_close() there's another inversion with i_mutex which is also acquired
> > > along the path for sysfs. And we can hardly get rid of it in the quota code.
> > >   Now none of these is a real deadlock as quota should never call
> > > print_warning() for sysfs (it doesn't use quota) but still it's nasty. I
> > > suppose tty_mutex is above i_mutex because of those sysfs calls and it
> > > seems sysfs must be called under tty_mutex because of races with
> > > init_dev(). So it's not easy to get rid of that dependency either.
> > 
> > maybe a far more serious option: Why on EARTH is the quota code going to
> > TTY's directly? That's just WRONG. Maybe it wasn't 10 years ago, but
> > nowadays most people use graphical user interfaces and the like...
>   We've been discussing this sometimes back in August ;)
> (http://lkml.org/lkml/2006/8/8/237) and we've decided to leave the code in.
> The only reason why I think it should stay in is the existence of quota
> softlimits. There it's nice to warn the user and there's no other way to
> propagate this information into userspace (as the write succeeds).
>   One solution would be to leave the warning to some userspace process
> (like warnquota) run from cron but still I'm not sure we should change the
> behavior.

or send a uevent or something


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