linux-kernel - Re: [PATCH 17/20] [SCSI] mpt3sas: Use alloc_ordered_workqueue() API instead of create_singlethread

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Date:	Mon, 15 Jun 2015 14:05:00 -0700
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Sreekanth Reddy <sreekanth.reddy@...gotech.com>
Cc:	Joe Lawrence <joe.lawrence@...atus.com>,
	"jejb@...nel.org" <jejb@...nel.org>,
	Christoph Hellwig <hch@...radead.org>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	Sathya Prakash <Sathya.Prakash@...gotech.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 17/20] [SCSI] mpt3sas: Use alloc_ordered_workqueue() API
 instead of create_singlethread_workqueue() API

On Mon, 2015-06-15 at 16:26 +0530, Sreekanth Reddy wrote:
> On Sat, Jun 13, 2015 at 2:33 AM, Joe Lawrence <joe.lawrence@...atus.com> wrote:
> > On 06/12/2015 05:42 AM, Sreekanth Reddy wrote:
> > ...
> >> +#if defined(alloc_ordered_workqueue)
> >> +     ioc->firmware_event_thread = alloc_ordered_workqueue(
> >> +             ioc->firmware_event_name, WQ_MEM_RECLAIM);
> >> +#else
> >> +             ioc->firmware_event_thread = create_singlethread_workqueue(
> >>           ioc->firmware_event_name);
> >> +#endif
> >
> > Hi Sreekanth,
> >
> > I think the upstream version of this code can safely assume
> > alloc_ordered_workqueue is defined, no?
> 
> yes, upstream version of this code can safely assume that
> alloc_ordered_workqueue is defined.
> 
> While working in-house, I observed that some of the older kernels
> doesn't defined this macro, so I have added this else section.

The driver has to be defined for the current kernel.  If you maintain a
backport, that's fine, but not in the upstream driver.  The reasons are
fairly pragmatic: this code in the #else clause can't be compiled so
it's just junk to the upstream driver and the static checkers will find
it and you'll attract a flock of patches removing dead code.

James


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