Re: [PATCH v3 0/2] Allow deferred execution of iomem_get_mapping()

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, Jul 30, 2021 at 07:06:26AM +0200, Greg Kroah-Hartman wrote:
> On Thu, Jul 29, 2021 at 11:32:33PM +0000, Krzysztof Wilczyński wrote:
> > Hello,
> > 
> > At the moment, the dependency on iomem_get_mapping() that is currently
> > used in the pci_create_resource_files() and pci_create_legacy_files()
> > stops us from completely retiring the late_initcall() that is used to
> > invoke pci_sysfs_init() when creating sysfs object for PCI devices.
> > 
> > This dependency on iomem_get_mapping() stops us from retiring the
> > late_initcall at the moment as when we convert dynamically added sysfs
> > objects, that are primarily added in the pci_create_resource_files() and
> > pci_create_legacy_files(), as these attributes are added before the VFS
> > completes its initialisation, and since most of the PCI devices are
> > typically enumerated in subsys_initcall this leads to a failure and an
> > Oops related to iomem_get_mapping() access.
> > 
> > See relevant conversations:
> >   https://lore.kernel.org/linux-pci/20210204165831.2703772-1-daniel.vetter@ffwll.ch/
> >   https://lore.kernel.org/linux-pci/20210313215747.GA2394467@bjorn-Precision-5520/
> > 
> > After some deliberation about the problem at hand, Dan Williams
> > suggested a solution to the problem, as per:
> >   https://lore.kernel.org/linux-pci/CAPcyv4i0y_4cMGEpNVShLUyUk3nyWH203Ry3S87BqnDJE0Rmxg@mail.gmail.com/
> > 
> > The idea is to defer execution of the iomem_get_mapping() to only when
> > the sysfs open callback is run, and thus removing the reliance of
> > fs_initcalls to complete before any other sub-system that uses the
> > iomem_get_mapping().
> > 
> > Currently, the PCI sub-system will benefit the most from this change
> > allowing for it to complete the transition from dynamically created to
> > static sysfs objects.
> > 
> > This series aims to take Dan Williams' idea through the finish line.
> > 
> > Related to:
> >   https://lore.kernel.org/linux-pci/20210527205845.GA1421476@bjorn-Precision-5520/
> >   https://lore.kernel.org/linux-pci/20210507102706.7658-1-danijel.slivka@amd.com/
> >   https://lore.kernel.org/linux-pci/20200716110423.xtfyb3n6tn5ixedh@pali/
> > 
> > 	Krzysztof
> > 
> 
> No objection from me on these, Bjorn, mind if I take them through my
> driver core tree?

That'd be great!

Is your tree immutable?  I'm hoping we can take advantage of this to
get rid of pci_sysfs_init(), which will fix a race that people seem to
be hitting frequently now [1].  I think Krzysztof is getting pretty
close.

[1] https://lore.kernel.org/r/m3eebg9puj.fsf@t19.piap.pl