linux-kernel - Re: 2.6.19-rc3-git7: scsi_device_unbusy: inconsistent lock state

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Message-ID: <20061030175400.GA31581@elte.hu>
Date:	Mon, 30 Oct 2006 18:54:00 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Arjan van de Ven <arjan@...radead.org>, Mark Lord <liml@....ca>,
	IDE/ATA development list <linux-ide@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.19-rc3-git7: scsi_device_unbusy: inconsistent lock state


* Jens Axboe <jens.axboe@...cle.com> wrote:

> > > things may be allocated from that path, so we pass gfp_mask around. I'll
> > > double check it tonight, but I don't currently see what could be wrong.
> > > Would lockdep complain about:
> > > 
> > >         spin_lock_irqsave(lock, flags);
> > >         ...
> > >         spin_unlock_irq(lock);
> > >         ...
> > >         spin_lock_irq(lock);
> > >         ...
> > >         spin_unlock_irqrestore(lock, flags);
> > 
> > this is fine for lockdep IF and only IF there is no "out lock" held
> > around this that requires irqs to be off. So if you do
> > 
> > spin_lock_irqsave(lock1, flags);
> > ...
> > spin_lock_irqsave(lock2, flags);
> > spin_unlock_irq(lock2)
> > ...
> > 
> > then lockdep WILL complain, and rightfully so, about a violation since
> > lock1 gets violated here ;)
> 
> Naturally, that is a bug fair and simple, nothing to do with lockdep.

well, finding such locking bugs is the main purpose of lockdep, so there 
is at least some connection i'd say ;-)

	Ingo
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