Date:	Wed, 19 Mar 2008 05:03:27 +0100
From:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Anders Eriksson <aeriksson@...tmail.fm>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Jens Axboe <jens.axboe@...cle.com>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux 2.6.25-rc4

On Wednesday 19 March 2008, Linus Torvalds wrote:
> 
> On Wed, 19 Mar 2008, Bartlomiej Zolnierkiewicz wrote:
> > 
> > Please take a closer look - my "real fix" _only_ affects WIN_SMART command
> > and _not_ vendor special ones (no, there are none vendor special commands
> > using the same opcode).
> 
> Oh, trust me, I understand your fix.
> 
> But the point is that your fix
> 
>  - doesn't fix any other commands (and there are tons of other commands 
>    people may be using)
> 
>  - and is totally pointless and isn't *needed* if we just fix this 
>    properly (ie we've never cared before, so why should we start caring 
>    now?).
> 
> See?
> 
> Fixing this properly is exactly what my patch did - it made the whole core 
> engine not really even care. Just like it used to.
> 
> > Call taskfile crap all you want [ ... ]
> 
> You're totally not listening or understanding.
> 
> I'm not calling taskfile crap as a concept.
> 
> I'm calling fragile code that fails unnecessarily crap.
> 
> See the difference?
> 
> The old "drive_cmd_intr()" code (that you deleted) was fundamentally more 
> robust than the taskfile code you replaced it with. 
> 
> And that's not just an opinion. It's a *fact*. It's why this bug showed up 
> in the first place. Code that used to work because it didn't even care all 
> that deeply about every single detail being set up just the way it wanted 
> got replaced by code that was fragile.
> 
> Do you see the difference?
> 
> If we have a choice between robust code that just "does the right thing" 
> even in the face of problems, and code that "stops working when you look 
> at it wrong", which one should we choose? Which one is the better code? 
> Which one is crap, and which one isn't?
> 
> The fact is, the old "drive_cmd_intr()" code was simply more robust.
> 
> So this is why I feel so strongly about this. Robust code is just about 
> the most important thing we can have in the kernel. Bugs will always 
> happen, but when they happen, we shouldn't just fall over dead. And that's 
> exactly what code robustness is all about.
> 
> So we should make the DRQ/ERR status bit handling robust in the face of 
> hardware and software that does odd things. Because we definitely have 
> seen cases of both. Sometimes it is hw that doesn't work the way the spec 
> requires, sometimes it's software that doesn't follow the spec 100%. It 
> doesn't matter.
> 
> And once the status bit handling is robust (like it _used_ to be!), only 
> *then* should we even ask ourself if we even care about having some random 
> tfargs.data_phase value for specific SMART command sub-cases.
> 
> My personal opinion is obviously that we simply shouldn't even care (since 
> we should now know that the driver doesn't care one way or the other), but 
> if you want to apply your patch despite it having absolutely no meaning, 
> that's your choice.
> 
> But the absolute first thing we should do is to make the code at least as 
> robust as it used to be, and preferably aim _higher_ in robustness rather 
> than lower!

OK, I got the point.

Your patch is more robust and we should go with it
(and thanks for fixing this bug!).

Bart
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