From: Bjorn Helgaas <helgaas@kernel.org>
To: "Pali Rohár" <pali@kernel.org>
Cc: "Oliver O'Halloran" <oohall@gmail.com>,
"Bjorn Helgaas" <bhelgaas@google.com>,
linux-pci <linux-pci@vger.kernel.org>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
"Lorenzo Pieralisi" <lorenzo.pieralisi@arm.com>,
"Gregory Clement" <gregory.clement@bootlin.com>,
"Andrew Lunn" <andrew@lunn.ch>,
"Krzysztof Wilczyński" <kw@linux.com>,
"Yinghai Lu" <yinghai@kernel.org>
Subject: Re: PCI: Race condition in pci_create_sysfs_dev_files
Date: Thu, 8 Oct 2020 14:59:07 -0500 [thread overview]
Message-ID: <20201008195907.GA3359851@bjorn-Precision-5520> (raw)
In-Reply-To: <20201007161434.GA3247067@bjorn-Precision-5520>
On Wed, Oct 07, 2020 at 11:14:34AM -0500, Bjorn Helgaas wrote:
> On Wed, Oct 07, 2020 at 10:14:00AM +0200, Pali Rohár wrote:
> > On Wednesday 07 October 2020 12:47:40 Oliver O'Halloran wrote:
> > > On Wed, Oct 7, 2020 at 10:26 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
> > > >
> > > > I'm not really a fan of this because pci_sysfs_init() is a bit of a
> > > > hack to begin with, and this makes it even more complicated.
> > > >
> > > > It's not obvious from the code why we need pci_sysfs_init(), but
> > > > Yinghai hinted [1] that we need to create sysfs after assigning
> > > > resources. I experimented by removing pci_sysfs_init() and skipping
> > > > the ROM BAR sizing. In that case, we create sysfs files in
> > > > pci_bus_add_device() and later assign space for the ROM BAR, so we
> > > > fail to create the "rom" sysfs file.
> > > >
> > > > The current solution to that is to delay the sysfs files until
> > > > pci_sysfs_init(), a late_initcall(), which runs after resource
> > > > assignments. But I think it would be better if we could create the
> > > > sysfs file when we assign the BAR. Then we could get rid of the
> > > > late_initcall() and that implicit ordering requirement.
> > >
> > > You could probably fix that by using an attribute_group to control
> > > whether the attribute shows up in sysfs or not. The .is_visible() for
> > > the group can look at the current state of the device and hide the rom
> > > attribute if the BAR isn't assigned or doesn't exist. That way we
> > > don't need to care when the actual assignment occurs.
> >
> > And cannot we just return e.g. -ENODATA (or other error code) for those
> > problematic sysfs nodes until late_initcall() is called?
>
> I really like Oliver's idea and I think we should push on that to see
> if it can be made to work. If so, we can remove the late_initcall()
> completely.
>
> > > > But I haven't tried to code it up, so it's probably more complicated
> > > > than this. I guess ideally we would assign all the resources before
> > > > pci_bus_add_device(). If we could do that, we could just remove
> > > > pci_sysfs_init() and everything would just work, but I think that's a
> > > > HUGE can of worms.
> > >
> > > I was under the impression the whole point of pci_bus_add_device() was
> > > to handle any initialisation that needed to be done after resources
> > > were assigned. Is the ROM BAR being potentially unassigned an x86ism
> > > or is there some bigger point I'm missing?
>
> We can't assign resources for each device as we enumerate it because
> we don't know what's in use by other devices yet to be enumerated.
> That part is generic, not x86-specific.
>
> The part that is x86-specific (or at least specific to systems using
> ACPI) is that the ACPI core doesn't reserve resources used by ACPI
> devices. Sometimes those resources are included in the PCI host
> bridge windows, and we don't want to assign them to PCI devices.
>
> I didn't trace this all the way, but the pcibios_assign_resources()
> and pnp_system_init() comments look relevant. It's a little concerning
> that they're both fs_initcalls() and the ordering looks important, but
> it would only be by accident of link ordering that pnp_system_init()
> happens first.
Pali, what's your thought on this? Do you plan to work on this
yourself? If not and if you can live with your workaround a while
longer, I think Krzysztof might be interested in taking a crack at it.
I would just hate to see you guys duplicate each others' work :)
Bjorn
next prev parent reply other threads:[~2020-10-08 19:59 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-16 11:04 PCI: Race condition in pci_create_sysfs_dev_files Pali Rohár
2020-08-14 8:08 ` Pali Rohár
2020-09-09 11:28 ` Pali Rohár
2020-10-05 8:20 ` Pali Rohár
2020-10-05 13:54 ` Bjorn Helgaas
2020-10-06 22:22 ` Bjorn Helgaas
2020-10-07 1:47 ` Oliver O'Halloran
2020-10-07 8:14 ` Pali Rohár
2020-10-07 16:14 ` Bjorn Helgaas
2020-10-08 19:59 ` Bjorn Helgaas [this message]
2020-10-09 8:08 ` Pali Rohár
2020-11-04 16:29 ` Pali Rohár
2020-11-15 6:19 ` Krzysztof Wilczyński
2020-11-15 12:10 ` Pali Rohár
2020-10-07 8:12 ` Pali Rohár
2021-04-07 14:25 ` Petr Štetiar
2021-04-07 14:51 ` Pali Rohár
2021-04-07 15:30 ` Petr Štetiar
2021-06-25 11:29 ` Koen Vandeputte
2021-06-25 11:54 ` Pali Rohár
2021-10-13 6:18 ` Dexuan-Linux Cui
2021-11-18 3:09 ` Krzysztof Wilczyński
2021-11-18 3:42 ` Dexuan Cui
2020-11-04 16:46 ` Pali Rohár
2021-04-07 14:41 ` Pali Rohár
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