linux-kernel - Re: [PATCH 1/2] kobject: remove kset from sysfs immediately in kset

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Message-ID: <CAErSpo5zWigf=b41uA=OBaFsCb3DNxXFj+2RoD1X8vSqTKDQ4g@mail.gmail.com>
Date:	Thu, 5 Dec 2013 17:34:54 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Veaceslav Falico <vfalico@...hat.com>,
	Russell King <linux@....linux.org.uk>,
	Neil Horman <nhorman@...driver.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Zdenek Kabelac <zkabelac@...hat.com>,
	Matt Domsch <Matt_Domsch@...l.com>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH 1/2] kobject: remove kset from sysfs immediately in kset_unregister()

On Thu, Dec 5, 2013 at 5:01 PM, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> On Tue, Dec 03, 2013 at 03:41:43PM -0700, Bjorn Helgaas wrote:
>> [+cc Matt, Tejun]
>>
>> On Tue, Dec 03, 2013 at 10:04:25AM -0800, Greg Kroah-Hartman wrote:
>> > On Tue, Oct 08, 2013 at 02:20:16PM -0600, Bjorn Helgaas wrote:
>> > > There's no explicit "unlink from sysfs" interface for ksets, so I think
>> > > callers of kset_unregister() expect the kset to be removed from sysfs
>> > > immediately, without waiting for the last reference to be released.
>> > >
>> > > This patch makes the sysfs removal happen immediately, so the caller may
>> > > create a new kset with the same name as soon as kset_unregister() returns.
>> > >
>> > > Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
>> >
>> > With the PCI MSI attribute change, this patch is no longer needed,
>> > right?
>>
>> Well, yes and no.  The attached patch extends Russell's delayed kobject
>> release to make the delay somewhat random.  I *think* that should be
>> valid, but correct me if I'm wrong.
>
> Heh, I like it, mind if I queue it up?

Sure, that'd be fine.  I'll resend these two patches with my sign-off
and updated changelogs.

>> With the random delay patch, it's easy to trigger the "sysfs: cannot
>> create duplicate filename" error, e.g., by unloading and reloading the
>> edd module, because the module unload only waits for the /sys/module/edd
>> object to be released.  Other objects, such as the /sys/firmware/edd
>> kset, may be released later.
>>
>> Modules like edd could be changed to explicitly call kobject_del() on
>> the kset kobject.  Maybe that's a better approach, so we consistently
>> use kobject_del() to remove things from sysfs.  But I don't know whether
>> it's really useful to allow the kset to hang around in sysfs after
>> kset_unregister(), and it's sort of subtle to track down problems like
>> this.
>>
>> Several other kset_unregister() callers have this situation, so if we
>> don't change it to call kobject_del() internally, maybe we should add a
>> note to Documentation/kobject.txt about calling kobject_del() first.
>> The existing hint only talks about using it when you need a two-stage
>> delete, which isn't really the case here.
>>
>> If we *do* decide to change kset_unregister(), I have an updated
>> documentation patch that makes it more clear that the release may
>> happen after kset_unregister() returns.
>
> Ok, I'll take this patch, it makes sense on the module unload path for
> example.  Thanks for the explanation.
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