linux-kernel - [PATCH 0/3] PCI: Fix race condition upon sysfs init

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Message-Id: <20230427142901.3570536-1-alexander.stein@ew.tq-group.com>
Date:   Thu, 27 Apr 2023 16:28:58 +0200
From:   Alexander Stein <alexander.stein@...tq-group.com>
To:     Bjorn Helgaas <bhelgaas@...gle.com>
Cc:     Alexander Stein <alexander.stein@...tq-group.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Korneliusz Osmenda <korneliuszo@...il.com>,
        Oliver Neukum <oneukum@...e.com>
Subject: [PATCH 0/3] PCI: Fix race condition upon sysfs init

Hi everyone,

this series is a totally different approach for fixing the sysfs init race
condition. The initial problem is stated at [1]. Previous proposals were
rejected ([2] and [3]). Here is what's happening

        CPU 0                                  CPU 1

                                        imx6_pcie_probe()
                                        dw_pcie_host_init()
                                        pci_host_probe()
                                        pci_scan_root_bus_bridge()
                                          pci_scan_child_bus_extend()
                                          pci_scan_slot()
                                          pci_scan_single_device()
                                          pci_device_add()
pci_sysfs_init()                          device_add()
  sysfs_initialized = 1;                  bus_add_device()
  for_each_pci_dev()                          ...
    pci_create_sysfs_dev_files()                  
                                        pci_bus_add_devices()
                                        pci_bus_add_device()
                                        pci_create_sysfs_dev_files()

Eventually calling pci_create_sysfs_dev_files() twice on the same pci_dev.
It's a very tight window, deeper PCIe trees increase that window during
host probe. Asynchronous PCIe host probe is a necessity
(PROBE_PREFER_ASYNCHRONOUS).

The first two patches are preparations for the last one actually fixing
the race. As functions like pci_create_sysfs_dev_files() are called from
externtal and internal to pci-sysfs, an internal version without checking
for sysfs_initialized is required.
For the fix a wait queue is introduced where all callers from external
callsites (regarding pci-sysfs.c) are waiting until pci_sysfs_init
initcall has finished and woken up all waiters.

A subtlety is that within __pci_create_sysfs_dev_files the resource files
(created by pci_sysfs_init) need to be removed, so they can be created
again from pci_host_probe call.

Best regards,
Alexander

Links:
[1] https://bugzilla.kernel.org/show_bug.cgi?id=215515
[2] https://lore.kernel.org/linux-pci/20230316091540.494366-1-alexander.stein@ew.tq-group.com/
[3] https://lore.kernel.org/linux-pci/20230316103036.1837869-1-alexander.stein@ew.tq-group.com/

Alexander Stein (3):
  PCI/sysfs: sort headers alphabetically
  PCI/sysfs: create private functions for
    pci_create_legacy_files/pci_create_sysfs_dev_files
  PCI/sysfs: Fix sysfs init race condition

 drivers/pci/pci-sysfs.c | 87 +++++++++++++++++++++++++----------------
 1 file changed, 53 insertions(+), 34 deletions(-)

-- 
2.34.1