From: "Pali Rohár" <pali@kernel.org>
To: "Bjorn Helgaas" <helgaas@kernel.org>,
"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>,
"Koen Vandeputte" <koen.vandeputte@citymesh.com>,
"Petr Štetiar" <ynezz@true.cz>
Subject: Re: PCI: Race condition in pci_create_sysfs_dev_files
Date: Wed, 7 Apr 2021 16:41:46 +0200 [thread overview]
Message-ID: <20210407144146.rl7x2h5l2cc3escy@pali> (raw)
In-Reply-To: <20200716110423.xtfyb3n6tn5ixedh@pali>
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.
Scratch this hack patch, it contains another new race condition.
The only way how to get rid of this race condition is either to protect
whole "sysfs_initialized" variable by mutex or by completely removing
"sysfs_initialized" variable and therefore also removing function
pci_create_sysfs_dev_files(). I'm for second variant.
prev parent reply other threads:[~2021-04-07 14:42 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
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 [this message]
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