On Thu, 2010-10-28 at 13:18 +0200, Boaz Harrosh wrote:
> On 10/28/2010 11:10 AM, Andi Kleen wrote:
> > 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;
> > }
> >
>
> I disagree with your approach this introduces a spin_unlock_irqrestore
> call site at every return, in the usually huge queuecommand.
>
> I'd say just do:
> - Rename XXX_queuecommand => __XXX_queuecommand_unlocked
> - Define new XXX_queuecommand
>
> int qc(struct scsi_cmnd *cmnd, ...)
> {
> unsigned long irqflags;
> int ret;
>
> spin_lock_irqsave(&cmnd->device->host->hostlock, irqflags);
> ret = __XXX_queuecommand_unlocked(cmnd, ...)
> spin_unlock_irqrestore(&cmnd->device->host->hostlock, irqflags);
> return ret;
> }
>
> Then when the driver is manually converted the __queuecommand_unlocked
> can be set into the scsi_host_template and the added function can
> be dropped.
>
I would have to agree that approach does make a bit more sense.. Now
can some brave soul (/me looks at ak) code another script to automate
this for the identified legacy LLDs cases that need push down..?
8-)
--nab
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