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Date:   Mon, 5 Oct 2020 08:54:29 -0500
From:   Bjorn Helgaas <helgaas@kernel.org>
To:     Pali =?iso-8859-1?Q?Roh=E1r?= <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>
Subject: Re: PCI: Race condition in pci_create_sysfs_dev_files
Message-ID: <20201005135429.GA3007344@bjorn-Precision-5520>
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In-Reply-To: <20201005082018.rowqpfifyyrilxma@pali>
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On Mon, Oct 05, 2020 at 10:20:18AM +0200, Pali Roh?r wrote:
> PING?

Sorry, I guess nobody has had the right combination of time, interest,
and knowledge to work on this.  I'll try to take a look this week.

> On Wednesday 09 September 2020 13:28:50 Pali Roh?r 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 Roh?r wrote:
> > > Hello! I would like to remind this issue which I reported month ago.
> > > 
> > > On Thursday 16 July 2020 13:04:23 Pali Roh?r 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.
> > > 
> > > > 
> > > > 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)
> > > >