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Date:	Thu, 28 Oct 2010 11:10:20 +0200
From:	Andi Kleen <ak@...ux.intel.com>
To:	James Bottomley <James.Bottomley@...e.de>
Cc:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>,
	Mike Anderson <andmike@...ux.vnet.ibm.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	Vasu Dev <vasu.dev@...ux.intel.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Mike Christie <michaelc@...wisc.edu>,
	Jens Axboe <jaxboe@...ionio.com>,
	James Smart <james.smart@...lex.com>,
	Andrew Vasquez <andrew.vasquez@...gic.com>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	Hannes Reinecke <hare@...e.de>,
	Joe Eykholt <jeykholt@...co.com>,
	Christoph Hellwig <hch@....de>,
	Jon Hawley <warthog9@...nel.org>,
	Brian King <brking@...ux.vnet.ibm.com>,
	Christof Schmitt <christof.schmitt@...ibm.com>,
	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>, julia@...u.dk
Subject: Re: [ANNOUNCE] Status of unlocked_qcmds=1 operation for .37

On Wed, Oct 27, 2010 at 09:27:38AM -0500, James Bottomley wrote:
> On Wed, 2010-10-27 at 09:53 +0200, Andi Kleen wrote:
> > > This sounds like a pretty reasonable compromise that I think is slightly
> > > less risky for the LLDs with the ghosts and cob-webs hanging off of
> > > them.
> > 
> > They won't get tested either next release cycle. Essentially
> > near nobody uses them.
> > 
> > > 
> > > What do you think..?
> > 
> > Standard linux practice is to simply push the locks down. That's a pretty
> > mechanical operation and shouldn't be too risky
> > 
> > With some luck you could even do it with coccinelle.
> 
> Precisely ... if we can do the push down now as a mechanical
> transformation we can put it in the current merge window as a low risk
> API change.  This gives us optimal exposure to the rc sequence to sort
> out any problems that arise (or drivers that got missed) with the lowest
> risk of such problems actually arising.  Given the corner cases and the
> late arrival of fixes, the serial number changes are just too risky for
> the current merge window.  Having an API that changes depending on a
> flag is also a high risk process because it's prone to further sources
> of error.

Here's a coccinelle script I came up with that does the push down.
It still adds a bogus empty line in front of the irqflags declaration
which I haven't managed to avoid yet. Other than the it seems
to DTRT on the SCSI drivers I tried.

-Andi


@ rule1 @
struct scsi_host_template t;
identifier qc;
@@
t.queuecommand = qc;

@ rule2 @
identifier rule1.qc;
identifier cmnd;
expression E;
statement S, S2;
@@
int qc(struct scsi_cmnd *cmnd, ...) 
{
	... when != S
+	unsigned long irqflags;

+	spin_lock_irqsave(&cmnd->device->host->hostlock, irqflags);
	S2
	...
+	spin_unlock_irqrestore(&cmnd->device->host->hostlock, irqflags);
	return E;
}



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