linux-kernel - Re: [PATCH v3 1/3] msi: free msi_desc entry only after we've released the kobject

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Message-ID: <20131126124719.GA11637@hmsreliant.think-freely.org>
Date:	Tue, 26 Nov 2013 07:47:19 -0500
From:	Neil Horman <nhorman@...driver.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Veaceslav Falico <vfalico@...hat.com>,
	linux-pci@...r.kernel.org, torvalds@...ux-foundation.org,
	tglx@...utronix.de, yinghai@...nel.org, Knut_Petersen@...nline.de,
	mingo@...nel.org, paulmck@...ux.vnet.ibm.com, fweisbec@...il.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] msi: free msi_desc entry only after we've
 released the kobject

On Mon, Nov 25, 2013 at 03:29:36PM -0800, Greg Kroah-Hartman wrote:
> On Mon, Nov 25, 2013 at 04:12:48PM -0700, Bjorn Helgaas wrote:
> > On Tue, Oct 29, 2013 at 11:30:30AM +0100, Veaceslav Falico wrote:
> > > Currently, we first do kobject_put(&entry->kobj) and the kfree(entry),
> > > however kobject_put() doesn't guarantee us that it was the last reference
> > > and that the kobj isn't used currently by someone else, so after we
> > > kfree(entry) with the struct kobject - other users will begin using the
> > > freed memory, instead of the actual kobject.
> > > 
> > > Fix this by using the kobject->release callback, which is called last when
> > > the kobject is indeed not used and is cleaned up - it's msi_kobj_release(),
> > > which can do the kfree(entry) safely (kobject_put/cleanup doesn't use the
> > > kobj itself after ->release() was called, so we're safe).
> > > 
> > > In case we've failed to create the sysfs directories - just kfree()
> > > it - cause we don't have the kobjects attached.
> > > 
> > > Also, remove the same functionality from populate_msi_sysfs(), cause on
> > > failure we anyway call free_msi_irqs(), which will take care of all the
> > > kobjects properly.
> > > 
> > > And add the forgotten pci_dev_put(pdev) in case of failure to register the
> > > kobject in populate_msi_sysfs().
> > > 
> > > CC: Bjorn Helgaas <bhelgaas@...gle.com>
> > > CC: Neil Horman <nhorman@...driver.com>
> > > CC: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > > CC: linux-pci@...r.kernel.org
> > > CC: linux-kernel@...r.kernel.org
> > > Signed-off-by: Veaceslav Falico <vfalico@...hat.com>
> > 
> > I'm still hoping that Greg (or somebody else; Greg already posted the bulk
> > of the work) will finish up the conversion to attributes, and that Neil
> > will confirm that works with no changes to irqbalance.  So I'm going to
> > drop these patches for now.  Poke me if we need to revive them.
> 
> Ah, sorry about that.  I'll redo my series, dropping the existing format
> and using the attribute-only code.  Give me a day or so, thanks for the
> reminder.
> 
> greg k-h
> 
Thank you greg, I'll make sure Irqbalance doesn't choke on the new format as
soon as you post them.

Neil

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