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Wed, 29 Apr 2026 20:04:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777493081; bh=ttY+1mHK9AUaFpm72RQJRVBgW0SdDDoYGSZPfSaYn18=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=M9Meet6zdZ092aa4T3HcHb7qbc9y2d7f0V3nvhcYbz7VpQsFYwmC7UJVoEjPi1HrZ 1s0gRx/lJVkhwvW9Zq3xpSigh3w9c7FeON2NpdzSn03NdUREW9KXxrVXdBNexmtV9K ls9FGE95CD7IQLdMYHj/etYTSCFanT6wYHdRCiugf1Th3rRfrso6NXvdS83wsHqfRy sMaC5l9P6Y3qiQI7+NWZ/khmEmnUv+1UoWcrVSYh9GZ4qEIRzA9jDPE3qydC4eBwE6 oesaYOz5RjyWWdayV0t18WECKRCApBbo7ftCyA+53ImFXKYmwZ5DzCDmeUzBgH0RyW NTURaN9BR5hpA== Date: Wed, 29 Apr 2026 15:04:39 -0500 From: Bjorn Helgaas To: Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= Cc: Bjorn Helgaas , Manivannan Sadhasivam , Lorenzo Pieralisi , Magnus Lindholm , Matt Turner , Richard Henderson , Christophe Leroy , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , Dexuan Cui , Krzysztof =?utf-8?Q?Ha=C5=82asa?= , Lukas Wunner , Oliver O'Halloran , Saurabh Singh Sengar , Shuan He , Srivatsa Bhat , Ilpo =?utf-8?B?SsOkcnZpbmVu?= , linux-pci@vger.kernel.org, linux-alpha@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, moubingquan , Ian <4dark@outlook.com>, Koba Ko , Koen Vandeputte , Pali =?utf-8?B?Um9ow6Fy?= , Artem Savkov , Korneliusz Osmenda , Alexander Stein Subject: Re: [PATCH v6 00/24] PCI: Convert all dynamic sysfs attributes to static Message-ID: <20260429200439.GA313340@bhelgaas> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260422161407.118748-1-kwilczynski@kernel.org> [+cc moubingquan, Ian, Koba, Krzysztof H, Koen, Pali, Artem, Korneliusz, Alexander +bcc vsd in case any of you can verify that this fixes the issue you reported] On Wed, Apr 22, 2026 at 04:13:43PM +0000, Krzysztof Wilczyński wrote: > Hello, > > This series converts every dynamically allocated PCI sysfs attribute to > a static const definition. After the full series, pci_sysfs_init() and > sysfs_initialized are gone, and every sysfs file is created by the > driver model at device_add() time. > > Currently, the PCI resource files (resourceN, resourceN_wc) and the > legacy bus files (legacy_io, legacy_mem) are created dynamically > from two unsynchronised paths: > > Path A: late_initcall > > pci_sysfs_init (late_initcall) > sysfs_initialized = 1 > for_each_pci_dev > pci_create_sysfs_dev_files > sysfs_create_bin_file (resourceN, resourceN_wc) > pci_find_next_bus > pci_create_legacy_files > sysfs_create_bin_file (legacy_io, legacy_mem) > > Path B: device registration / hotplug > > pci_bus_add_devices > pci_bus_add_device > pci_create_sysfs_dev_files > if (!sysfs_initialized) return <- only guard > sysfs_create_bin_file (resourceN, resourceN_wc) > > On most ACPI systems this does not race because PCI enumeration > completes at subsys_initcall time, before pci_sysfs_init() runs: > > subsys_initcall (level 4): > acpi_pci_root_add > pci_bus_add_device > pci_create_sysfs_dev_files > if (!sysfs_initialized) <- not yet set > return -EACCES > > late_initcall (level 7): > pci_sysfs_init > sysfs_initialized = 1 > for_each_pci_dev > pci_create_sysfs_dev_files <- creates the files, no race > > On Devicetree platforms the host controller is a platform driver that > probes via the driver model, often on a workqueue, and overlaps with the > late_initcall: > > CPU 0 (late_initcall) CPU 1 (driver probe) > --------------------------- ---------------------------- > pci_sysfs_init() > sysfs_initialized = 1 > for_each_pci_dev(pdev) pci_bus_add_device(pdev) > pci_create_sysfs_dev_files() pci_create_sysfs_dev_files() > sysfs_create_bin_file() sysfs_create_bin_file() > -> "duplicate filename" > > The same happens on ACPI when probing is asynchronous (hv_pci on > Azure, RISC-V with ACPI). > > The duplicate causes sysfs_create_bin_file() to fail with -EEXIST. > pci_create_resource_files() then calls pci_remove_resource_files() in > its error unwind, tearing down files the other thread created and > still references through pdev->res_attr[]. This has caused kernel > panics on i.MX6 and boot failures on other platforms. > > Several different fixes have been proposed over the years: reordering > the sysfs_initialized assignment, adding locks, checking > pci_dev_is_added(), setting pdev->res_attr[] to NULL after kfree > (which only prevents a double-free on the teardown path, not the > error unwind removing the other thread's files). None would address the > root cause. > > This has been reported a few times: > > - https://lore.kernel.org/linux-pci/20250702155112.40124-1-heshuan@bytedance.com/ > - https://lore.kernel.org/linux-pci/b51519d6-ce45-4b6d-8135-c70169bd110e@h-partners.com/ > - https://lore.kernel.org/linux-pci/1702093576-30405-1-git-send-email-ssengar@linux.microsoft.com/ > - https://lore.kernel.org/linux-pci/SY0P300MB04687548090B73E40AF97D8897B82@SY0P300MB0468.AUSP300.PROD.OUTLOOK.COM/ > - https://lore.kernel.org/linux-pci/20230105174736.GA1154719@bhelgaas/ > - https://lore.kernel.org/linux-pci/m3eebg9puj.fsf@t19.piap.pl/ > - https://lore.kernel.org/linux-pci/20200716110423.xtfyb3n6tn5ixedh@pali/ > - https://lore.kernel.org/linux-pci/1366196798-15929-1-git-send-email-artem.savkov@gmail.com/ > - https://bugzilla.kernel.org/show_bug.cgi?id=215515 > - https://bugzilla.kernel.org/show_bug.cgi?id=216888 Seems like some or all of these should be mentioned in the relevant patch as "Closes:" tags? > With static attributes the driver model creates sysfs entries once per > device at device_add() time, under the device lock, eliminating the > late_initcall iteration and the race along with it.