[+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@xxxxxxxxxxxxxx/ > > > 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) > > >
