Re: [PATCH] PCI: Also set up legacy files only after sysfs init

On Wed, Feb 10, 2021 at 10:40 PM Bjorn Helgaas [off-list ref] wrote:

On Fri, Feb 05, 2021 at 02:36:32PM +0100, Daniel Vetter wrote:

quoted

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
no problem, but in the next patch I want to wire up iomem revoke
support. That needs the vfs up and running already to make sure that
iomem_get_mapping() works.

Wire it up exactly like the existing code in
pci_create_sysfs_dev_files(). Note that pci_remove_legacy_files()
doesn't need a check since the one for pci_bus->legacy_io is
sufficient.

An alternative solution would be to implement a callback in sysfs to
set up the address space from iomem_get_mapping() when userspace calls
mmap(). This also works, but Greg didn't really like that just to work
around an ordering issue when the kernel loads initially.

v2: Improve commit message (Bjorn)

Signed-off-by: Daniel Vetter <redacted>

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

I wish we weren't extending a known-racy mechanism to do this, but at
least we're not *adding* a brand new race.

Yeah it's not great. Thanks for looking at both again, I'll fix up the
typos on the 2nd one and merge them both.

Cheers, Daniel

quoted

Cc: Stephen Rothwell <redacted>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Kees Cook <redacted>
Cc: Dan Williams <redacted>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Jérôme Glisse <redacted>
Cc: Jan Kara <jack@suse.cz>
Cc: Dan Williams <redacted>
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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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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