Re: [ANNOUNCE] Status of unlocked_qcmds=1 operation for .37

[Andi Kleen <ak@linux.intel.com>]

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;
}