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In December 2002, historic commit https://git.kernel.org/tglx/history/c/bec7aa00ffe5 ("[PATCH] more module warning fixes") amended the PCI hotplug core to acquire a reference on the hotplug driver module when a sysfs attribute is accessed. That was necessary because back in the day, sysfs code did not take any precautions to prevent module unloading when an attribute was accessed. Soon after in July 2003, historic commit https://git.kernel.org/tglx/history/c/1cf6d20f6078 ("[PATCH] SYSFS: add module referencing to sysfs attribute files.") addressed that deficiency. But the commit neglected to remove the now unnecessary reference acquisition from the PCI hotplug core. The commit acquired a module reference for the entire duration between open() and close() of a sysfs attribute. This made it impossible to unload a module while attributes were kept open by user space. That's possible today: When a hotplug driver module is unloaded, it removes sysfs attributes of all its hotplug slots by calling pci_hp_del(). This will wait for any concurrent user space operation to finish: pci_hp_del() fs_remove_slot() sysfs_remove_file() sysfs_remove_file_ns() kernfs_remove_by_name_ns() __kernfs_remove() kernfs_drain() A user space operation such as read() briefly acquires a reference on the attribute with kernfs_get_active(). kernfs_drain() waits until all such references are released before allowing attribute removal. Once the attribute is removed, any subsequent user space operation on a still open attribute file will return -ENODEV. Thus, reference acquisition by the PCI hotplug core is still unnecessary today. So drop it at long last. Link: https://lore.kernel.org/r/ed950fa2722967be4491146c7b867c1e7be11d37.1740501868.git.lukas@wunner.de Signed-off-by: Lukas Wunner <lukas@wunner.de> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.