From: Bjorn Helgaas <helgaas@kernel.org>
To: "Pali Rohár" <pali@kernel.org>
Cc: "Bjorn Helgaas" <bhelgaas@google.com>,
linux-pci@vger.kernel.org, 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: Tue, 6 Oct 2020 17:22:22 -0500 [thread overview]
Message-ID: <20201006222222.GA3221382@bjorn-Precision-5520> (raw)
In-Reply-To: <20200909112850.hbtgkvwqy2rlixst@pali>
[+cc Krzysztof, Yinghai]
On Wed, Sep 09, 2020 at 01:28:50PM +0200, Pali Rohár wrote:
> Hello! I'm adding more people to loop.
>
> Can somebody look at these race conditions and my patch?
>
> On Friday 14 August 2020 10:08:24 Pali Rohár wrote:
> > Hello! I would like to remind this issue which I reported month ago.
> >
> > On Thursday 16 July 2020 13:04:23 Pali Rohár wrote:
> > > Hello Bjorn!
> > >
> > > I see following error message in dmesg which looks like a race condition:
> > >
> > > sysfs: cannot create duplicate filename '/devices/platform/soc/d0070000.pcie/pci0000:00/0000:00:00.0/config'
> > >
> > > I looked at it deeper and found out that in PCI subsystem code is race
> > > condition between pci_bus_add_device() and pci_sysfs_init() calls. Both
> > > of these functions calls pci_create_sysfs_dev_files() and calling this
> > > function more times for same pci device throws above error message.
> > >
> > > There can be two different race conditions:
> > >
> > > 1. pci_bus_add_device() called pcibios_bus_add_device() or
> > > pci_fixup_device() but have not called pci_create_sysfs_dev_files() yet.
> > > Meanwhile pci_sysfs_init() is running and pci_create_sysfs_dev_files()
> > > was called for newly registered device. In this case function
> > > pci_create_sysfs_dev_files() is called two times, ones from
> > > pci_bus_add_device() and once from pci_sysfs_init().
> > >
> > > 2. pci_sysfs_init() is called. It first sets sysfs_initialized to 1
> > > which unblock calling pci_create_sysfs_dev_files(). Then another bus
> > > registers new PCI device and calls pci_bus_add_device() which calls
> > > pci_create_sysfs_dev_files() and registers sysfs files. Function
> > > pci_sysfs_init() continues execution and calls function
> > > pci_create_sysfs_dev_files() also for this newly registered device. So
> > > pci_create_sysfs_dev_files() is again called two times.
> > >
> > >
> > > I workaround both race conditions I created following hack patch. After
> > > applying it I'm not getting that 'sysfs: cannot create duplicate filename'
> > > error message anymore.
> > >
> > > Can you look at it how to fix both race conditions in proper way?
> >
> > Is this workaround diff enough? Or are you going to prepare
> > something better?
> >
> > Please let me know if I should send this diff as regular patch.
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.
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.
[1] https://lore.kernel.org/linux-pci/CAE9FiQWBXHgz-gWCmpWLaBOfQQJwtRZemV6Ut9GVw_KJ-dTGTA@mail.gmail.com/
> > > diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
> > > index 8e40b3e6da77..691be2258c4e 100644
> > > --- a/drivers/pci/bus.c
> > > +++ b/drivers/pci/bus.c
> > > @@ -316,7 +316,7 @@ void pci_bus_add_device(struct pci_dev *dev)
> > > */
> > > pcibios_bus_add_device(dev);
> > > pci_fixup_device(pci_fixup_final, dev);
> > > - pci_create_sysfs_dev_files(dev);
> > > + pci_create_sysfs_dev_files(dev, false);
> > > pci_proc_attach_device(dev);
> > > pci_bridge_d3_update(dev);
> > >
> > > diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> > > index 6d78df981d41..b0c4852a51dd 100644
> > > --- a/drivers/pci/pci-sysfs.c
> > > +++ b/drivers/pci/pci-sysfs.c
> > > @@ -1328,13 +1328,13 @@ static int pci_create_capabilities_sysfs(struct pci_dev *dev)
> > > return retval;
> > > }
> > >
> > > -int __must_check pci_create_sysfs_dev_files(struct pci_dev *pdev)
> > > +int __must_check pci_create_sysfs_dev_files(struct pci_dev *pdev, bool sysfs_initializing)
> > > {
> > > int retval;
> > > int rom_size;
> > > struct bin_attribute *attr;
> > >
> > > - if (!sysfs_initialized)
> > > + if (!sysfs_initializing && !sysfs_initialized)
> > > return -EACCES;
> > >
> > > if (pdev->cfg_size > PCI_CFG_SPACE_SIZE)
> > > @@ -1437,18 +1437,21 @@ void pci_remove_sysfs_dev_files(struct pci_dev *pdev)
> > > static int __init pci_sysfs_init(void)
> > > {
> > > struct pci_dev *pdev = NULL;
> > > - int retval;
> > > + int retval = 0;
> > >
> > > - sysfs_initialized = 1;
> > > for_each_pci_dev(pdev) {
> > > - retval = pci_create_sysfs_dev_files(pdev);
> > > + if (!pci_dev_is_added(pdev))
> > > + continue;
> > > + retval = pci_create_sysfs_dev_files(pdev, true);
> > > if (retval) {
> > > pci_dev_put(pdev);
> > > - return retval;
> > > + goto out;
> > > }
> > > }
> > >
> > > - return 0;
> > > +out:
> > > + sysfs_initialized = 1;
> > > + return retval;
> > > }
> > > late_initcall(pci_sysfs_init);
> > >
> > > diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> > > index 6d3f75867106..304294c7171e 100644
> > > --- a/drivers/pci/pci.h
> > > +++ b/drivers/pci/pci.h
> > > @@ -19,7 +19,7 @@ bool pcie_cap_has_rtctl(const struct pci_dev *dev);
> > >
> > > /* Functions internal to the PCI core code */
> > >
> > > -int pci_create_sysfs_dev_files(struct pci_dev *pdev);
> > > +int pci_create_sysfs_dev_files(struct pci_dev *pdev, bool sysfs_initializing);
> > > void pci_remove_sysfs_dev_files(struct pci_dev *pdev);
> > > #if !defined(CONFIG_DMI) && !defined(CONFIG_ACPI)
> > > static inline void pci_create_firmware_label_files(struct pci_dev *pdev)
> > >
next prev parent reply other threads:[~2020-10-06 22:22 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 [this message]
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
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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