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.
