Re: [PATCH 1/2] PCI: also set up legacy files only after sysfs init

Pali Rohár
2021-02-04T22:25:21Z

On Thursday 04 February 2021 15:50:19 Bjorn Helgaas wrote:
> [+cc Oliver, Pali, Krzysztof]

Just to note that extending or using sysfs_initialized introduces
another race condition into kernel code which results in PCI fatal
errors. Details are in email discussion which Bjorn already sent.

> s/also/Also/ in subject
>
> On Thu, Feb 04, 2021 at 05:58:30PM +0100, Daniel Vetter wrote:
> > We are already doing this for all the regular sysfs files on PCI
> > devices, but not yet on the legacy io files on the PCI buses. Thus far
> > now problem, but in the next patch I want to wire up iomem revoke
> > support. That needs the vfs up an running already to make so that
> > iomem_get_mapping() works.
>
> s/now problem/no problem/
> s/an running/and running/
> s/so that/sure that/ ?
>
> iomem_get_mapping() doesn't exist; I don't know what that should be.
>
> > Wire it up exactly like the existing code. Note that
> > pci_remove_legacy_files() doesn't need a check since the one for
> > pci_bus->legacy_io is sufficient.
>
> I'm not sure exactly what you mean by "the existing code." I could
> probably figure it out, but it would save time to mention the existing
> function here.
>
> This looks like another instance where we should really apply Oliver's
> idea of converting these to attribute_groups [1].
>
> The cover letter mentions options discussed with Greg in [2], but I
> don't think the "sysfs_initialized" hack vs attribute_groups was part
> of that discussion.
>
> It's not absolutely a show-stopper, but it *is* a shame to extend the
> sysfs_initialized hack if attribute_groups could do this more cleanly
> and help solve more than one issue.
>
> Bjorn
>
> [1] https://lore.kernel.org/r/CAOSf1CHss03DBSDO4PmTtMp0tCEu5kScn704ZEwLKGXQzBfqaA@mail.gmail.com
> [2] https://lore.kernel.org/dri-devel/CAKMK7uGrdDrbtj0OyzqQc0CGrQwc2F3tFJU9vLfm2jjufAZ5YQ@mail.gmail.com/
>
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > Cc: Stephen Rothwell <sfr@canb.auug.org.au>
> > Cc: Jason Gunthorpe <jgg@ziepe.ca>
> > Cc: Kees Cook <keescook@chromium.org>
> > Cc: Dan Williams <dan.j.williams@intel.com>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: John Hubbard <jhubbard@nvidia.com>
> > Cc: Jérôme Glisse <jglisse@redhat.com>
> > Cc: Jan Kara <jack@suse.cz>
> > Cc: Dan Williams <dan.j.williams@intel.com>
> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Cc: linux-mm@kvack.org
> > Cc: linux-arm-kernel@lists.infradead.org
> > Cc: linux-samsung-soc@vger.kernel.org
> > Cc: linux-media@vger.kernel.org
> > Cc: Bjorn Helgaas <bhelgaas@google.com>
> > Cc: linux-pci@vger.kernel.org
> > ---
> > drivers/pci/pci-sysfs.c | 7 +++++++
> > 1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> > index fb072f4b3176..0c45b4f7b214 100644
> > --- a/drivers/pci/pci-sysfs.c
> > +++ b/drivers/pci/pci-sysfs.c
> > @@ -927,6 +927,9 @@ void pci_create_legacy_files(struct pci_bus *b)
> > {
> > int error;
> >
> > + if (!sysfs_initialized)
> > + return;
> > +
> > b->legacy_io = kcalloc(2, sizeof(struct bin_attribute),
> > GFP_ATOMIC);
> > if (!b->legacy_io)
> > @@ -1448,6 +1451,7 @@ void pci_remove_sysfs_dev_files(struct pci_dev *pdev)
> > static int __init pci_sysfs_init(void)
> > {
> > struct pci_dev *pdev = NULL;
> > + struct pci_bus *pbus = NULL;
> > int retval;
> >
> > sysfs_initialized = 1;
> > @@ -1459,6 +1463,9 @@ static int __init pci_sysfs_init(void)
> > }
> > }
> >
> > + while ((pbus = pci_find_next_bus(pbus)))
> > + pci_create_legacy_files(pbus);
> > +
> > return 0;
> > }
> > late_initcall(pci_sysfs_init);
> > --
> > 2.30.0
> >
> >
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