linux-kernel - Re: [PATCH 7/7] driver-core : convert semaphore to mutex in struct class

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Date:	Fri, 18 Jan 2008 17:07:40 +0800
From:	"Dave Young" <hidave.darkstar@...il.com>
To:	"Jarek Poplawski" <jarkao2@...il.com>
Cc:	"Kay Sievers" <kay.sievers@...y.org>,
	"Alan Stern" <stern@...land.harvard.edu>,
	"Greg KH" <gregkh@...e.de>, stefanr@...6.in-berlin.de,
	"David Brownell" <david-b@...bell.net>,
	"Kernel development list" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 7/7] driver-core : convert semaphore to mutex in struct class

On Jan 18, 2008 4:23 PM, Jarek Poplawski <jarkao2@...il.com> wrote:
> On Fri, Jan 18, 2008 at 03:48:02PM +0800, Dave Young wrote:
> > On Jan 18, 2008 3:38 PM, Jarek Poplawski <jarkao2@...il.com> wrote:
> ...
> > > IMHO, it would be nice to get the real state of current lockdep
> > > problems here to figure out if there is any chance to do this right &
> > > without any warnings with current lockdep. If I got it right from
> > > earlier threads it might be impossible with USB, at least.
> >
> > I don't think so, usb doesn't be affected by struct class mutex, they
> > only use the lock of struct device. As I replied before, the lockdep
> > issue exist only between class_interface and class_device.
>
> OK, but I've meant possibility of changing their own semaphores later.
>
> > > So, since I think these nesting levels seem to be wrong in 7/7 patch,
> > > maybe it's better to exclude it from this patchset, and to try this as
> > > testing for some time.
> >
> > I may file the updated patch with more nesting changes and test it of
> > course. Actually I should have done it, thanks.
> ...
> > 1) Using CLASS_NORMAL/CLASS_PARENT/CLASS_CHILD will be enough.
> > or
> > 2) Simply add SINGLE_LEVEL_NESTING in class_device_add and other
> > class_device functions because it is the only possible nest-lock place
> > as I know.
>
> If SINGLE_LEVEL_NESTING is enough? (means 2 levels total)

I think so.

>
> I think you should more care about real (logical) relations here, than
> what's enough to get rid of lockdep warnings.

You are quite right, thanks.

>
> Since there are not so much of these changes, you can try both
> variants.

Will do.

>I'll be glad to look at this - maybe I'll mangage to figure
> out BTW, what it's all about...
>
> Jarek P.
>
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