linux-kernel - Re: [PATCH 01/12] libiscsi: Convert to host_lock less w/ interrupts disabled internally

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Message-ID: <20101220020758.GK1263@parisc-linux.org>
Date:	Sun, 19 Dec 2010 19:07:59 -0700
From:	Matthew Wilcox <matthew@....cx>
To:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
Cc:	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	James Bottomley <James.Bottomley@...e.de>,
	Jeff Garzik <jeff@...zik.org>, Christoph Hellwig <hch@....de>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	Hannes Reinecke <hare@...e.de>,
	Mike Christie <michaelc@...wisc.edu>
Subject: Re: [PATCH 01/12] libiscsi: Convert to host_lock less w/
	interrupts disabled internally

On Sun, Dec 19, 2010 at 05:22:06PM -0800, Nicholas A. Bellinger wrote:
> Actually sorry, Mike Christie did already make a clarification on this
> subject here:
> 
> http://marc.info/?l=linux-scsi&m=129010439421506&w=2
> 
> I had originally thought the same that session->lock should be using
> some flavour of spin_lock_irq*() as well, but apparently this is not the
> case for libiscsi.

Right, so it seems.  "the session lock is just locked in softirqs/timers"
means that it does need to be the _bh() version of spin_lock though.

I'm actually not sure ... is it safe to use the _bh versions in BH
context?  I think it is because the preempt count is nested, unlike the
_irq variants of spinlocks.

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."
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