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Subject: Re: 2.6.19-rc3-git7: scsi_device_unbusy: inconsistent lock state
From: Arjan van de Ven <arjan@infradead.org>
To: Jens Axboe <jens.axboe@oracle.com>
Cc: Mark Lord <liml@rtr.ca>,
       IDE/ATA development list <linux-ide@vger.kernel.org>,
       Linux Kernel <linux-kernel@vger.kernel.org>, mingo@elte.hu
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Organization: Intel International BV
Date: Mon, 30 Oct 2006 17:31:55 +0100
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> > 
> > 
> >  [<c0219091>] cfq_set_request+0x351/0x3b0
> >  [<c020c7fc>] elv_set_request+0x1c/0x40
> >  [<c020fcff>] get_request+0x23f/0x270
> >  [<c0210537>] get_request_wait+0x27/0x120
> >  [<c02107ca>] __make_request+0x5a/0x350
> >  [<c020f40f>] generic_make_request+0x16f/0x220
> >  [<c02117e4>] submit_bio+0x64/0x110
> > 
> > now cfq_set_request() uses several inlines which muddies the situation,
> > but lockdep claims one of them is not done correctly. (eg either it
> > takes the lock incorrectly or something does spin_unlock_irq while the
> > lock is held)
> 
> It's not really inlined trickery, the trace is exactly as printed.

what I meant is that cfq_set_request() calls a few inlines that also
take locks so it might be one of those instead

>  A few
> 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 ;)


-- 
if you want to mail me at work (you don't), use arjan (at) linux.intel.com
Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org

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