linux-kernel - Re: [RFC][PATCH] spinlock: Kill spin_unlock

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Date:	Fri, 7 Jan 2011 16:13:53 -0500
From:	Jeff Garzik <jeff@...zik.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <npiggin@...nel.dk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Chris Mason <chris.mason@...cle.com>,
	Frank Rowand <frank.rowand@...sony.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mike Galbraith <efault@....de>,
	Oleg Nesterov <oleg@...hat.com>, Paul Turner <pjt@...gle.com>,
	Jens Axboe <axboe@...nel.dk>,
	Yong Zhang <yong.zhang0@...il.com>,
	linux-kernel@...r.kernel.org,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Linux-Arch <linux-arch@...r.kernel.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	"IDE/ATA development list" <linux-ide@...r.kernel.org>
Subject: Re: [RFC][PATCH] spinlock: Kill spin_unlock_wait()

On Fri, Jan 7, 2011 at 4:01 PM, Tejun Heo <tj@...nel.org> wrote:
> On Thu, Jan 06, 2011 at 07:26:35PM +0100, Peter Zijlstra wrote:
>> Jeff, Tejun, could you look at the ata-eh thing, then I'll put sorting
>> through the futex thing on my todo list.
>
> Hmm... I think the ->eng_timeout path is already dead.  We no longer
> have any in-kernel implementation, so killing spin_unlock_wait()
> should be fine.  I'll follow up with removal of the unused callback.

Unfortunately...  libsas continues to avoid the new EH :(

It's a hairy mess to untangle, too.  libata does proper error handling
of ATA device errors, notably NCQ error handling, which libsas sorely
misses.  But libata new EH assumes a bit too much about "owning" the
entirety of the EH process.  These assumptions are proper for wholly
ATA drivers (drivers/ata/*) where new EH can drive the EH process, but
in the SAS situation, a phy in SATA mode is simply a subset of a
larger set of EH conditions that must be handled.

Thus libsas uses the ancient libata hook ->phy_reset and lacks ->error_handler.

I think libata's old-EH path is entirely SAS-specific at this point.

     Jeff


P.S.  Note that libsas and ipr are peers; thus ipr driver also uses old EH.
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