linux-kernel - Re: [RFC: 2.6.19 patch] let PCI_MULTITHREAD

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Message-ID: <20061027222326.GC27968@stusta.de>
Date:	Sat, 28 Oct 2006 00:23:26 +0200
From:	Adrian Bunk <bunk@...sta.de>
To:	Greg KH <greg@...ah.com>
Cc:	Stephen Hemminger <shemminger@...l.org>,
	Andrew Morton <akpm@...l.org>, Matthew Wilcox <matthew@....cx>,
	Linus Torvalds <torvalds@...l.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Pavel Machek <pavel@....cz>, linux-pci@...ey.karlin.mff.cuni.cz
Subject: Re: [RFC: 2.6.19 patch] let PCI_MULTITHREAD_PROBE depend on BROKEN

On Fri, Oct 27, 2006 at 10:07:48AM -0700, Greg KH wrote:
> On Thu, Oct 26, 2006 at 07:11:31PM -0700, Stephen Hemminger wrote:
> > On Thu, 26 Oct 2006 18:28:38 -0700
> > Andrew Morton <akpm@...l.org> wrote:
> > 
> > > On Thu, 26 Oct 2006 19:20:58 -0600
> > > Matthew Wilcox <matthew@....cx> wrote:
> > > 
> > > > On Fri, Oct 27, 2006 at 03:02:52AM +0200, Adrian Bunk wrote:
> > > > > PCI_MULTITHREAD_PROBE is an interesting feature, but in it's current 
> > > > > state it seems to be more of a trap for users who accidentally
> > > > > enable it.
> > > > > 
> > > > > This patch lets PCI_MULTITHREAD_PROBE depend on BROKEN for 2.6.19.
> > > > > 
> > > > > The intention is to get this patch reversed in -mm as soon as it's in 
> > > > > Linus' tree, and reverse it for 2.6.20 or 2.6.21 after the fallout of 
> > > > > in-kernel problems PCI_MULTITHREAD_PROBE causes got fixed.
> > > > 
> > > > People who enable features clearly marked as EXPERIMENTAL deserve what
> > > > they get, IMO.
> > > 
> > > It's not the impact on "people" which is of concern - it's the impact on
> > > kernel developers - specifically those who spend time looking at bug
> > > reports :(
> > 
> > Either it is broken and should be removed, or is barely working and
> > should be fixed. If Greg wants to take bug reports then it can stay.
> 
> I want to keep taking bug reports.
> 
> I've found only 1 real bug from all of this.  The pci MSI initialization
> issue.  It's on my queue of things to fix.  Andrew has also sent me
> another "interesting" patch about making sure devices are found by the
> time we hit another init level which I'll see about adding too.
> 
> But that MSI bug was a real bug, which is good to have found.  It's also
> found other real bugs in other subsystems that could easily be hit by
> other users.
> 
> So no, this should not be marked BROKEN.
> 
> It's a very experimental feature, as the help text says.  If you can
> think of any harsher language to put in that text, please let me know.

The problem is that if only 1 out of 100 people who are compiling a 
kernel accidentally enable this option, linux-kernel will be swamped 
with bug reports...

If it shouldn't be enabled by users, the only correct language is a 
dependency on BROKEN.

And it doesn't matter whether PCI_MULTITHREAD_PROBE itself is buggy or 
whether it only exposes latent bugs in other subsystems - the effect is 
the same.

> And yes, there also has been a proposed change to the driver core to fix
> up how the multi-thread stuff works that looks very good, but it's down
> in my queue that I'm trying to catch up on right now.
> 
> So consider this a NAK for this change.
> 
> thanks,
> 
> greg k-h

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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