On Fri, Feb 5, 2021 at 11:04 AM Pali Rohár <pali@xxxxxxxxxx> wrote: > > On Friday 05 February 2021 10:59:50 Daniel Vetter wrote: > > On Thu, Feb 4, 2021 at 11:24 PM Pali Rohár <pali@xxxxxxxxxx> wrote: > > > > > > 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. > > > > Yeah I wondered why this doesn't race. > > It races, but with smaller probability. I have not seen this race > condition on x86. But I was able to reproduce it with native PCIe > drivers on ARM64 (Marvell Armada 3720; pci-aardvark). In mentioned > discussion I wrote when this race condition happen. But I understand > that it is hard to simulate it. btw I looked at your patch, and isn't that just reducing the race window? I think we have a very similar problem in drm, where the drm_dev_register() for the overall device (which also registers all drm_connector) can race with the hotplug of an individual connector in drm_connector_register() which is hotplugged at runtime. I went with a per-connector registered boolean + a lock to make sure that really only one of the two call paths can end up registering the connector. Part of registering connectors is setting up sysfs files, so I think it's exactly the same problem as here. Cheers, Daniel > > > but since the history goes back > > to pre-git times I figured it would have been addressed somehow > > already if it indeed does race. > > -Daniel > > > > > > 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@xxxxxxxxxxxxxx > > > > [2] https://lore.kernel.org/dri-devel/CAKMK7uGrdDrbtj0OyzqQc0CGrQwc2F3tFJU9vLfm2jjufAZ5YQ@xxxxxxxxxxxxxx/ > > > > > > > > > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx> > > > > > Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> > > > > > Cc: Jason Gunthorpe <jgg@xxxxxxxx> > > > > > Cc: Kees Cook <keescook@xxxxxxxxxxxx> > > > > > Cc: Dan Williams <dan.j.williams@xxxxxxxxx> > > > > > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > > > > > Cc: John Hubbard <jhubbard@xxxxxxxxxx> > > > > > Cc: Jérôme Glisse <jglisse@xxxxxxxxxx> > > > > > Cc: Jan Kara <jack@xxxxxxx> > > > > > Cc: Dan Williams <dan.j.williams@xxxxxxxxx> > > > > > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > > > > > Cc: linux-mm@xxxxxxxxx > > > > > Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > > > > > Cc: linux-samsung-soc@xxxxxxxxxxxxxxx > > > > > Cc: linux-media@xxxxxxxxxxxxxxx > > > > > Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx> > > > > > Cc: linux-pci@xxxxxxxxxxxxxxx > > > > > --- > > > > > 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 > > > > > > > > > > > > > > > _______________________________________________ > > > > > linux-arm-kernel mailing list > > > > > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > > > > > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel > > > > > > > > -- > > Daniel Vetter > > Software Engineer, Intel Corporation > > http://blog.ffwll.ch -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
