Re: [PATCH v3] PCI/proc: Fix race between pci_proc_init() and pci_bus_add_device()

["Krzysztof Wilczyński" <kwilczynski@kernel.org>]

Hello,

[...]
> > Thus, extract the bus procfs directory creation from
> > pci_proc_attach_device() into a new pci_proc_attach_bus() function,
> > and call it from the two bus creation paths: pci_register_host_bridge()
> > for root buses and pci_alloc_child_bus() for child buses.  These are
> > the only two callers of pci_alloc_bus(), so for buses created after
> > proc_initialized is set, bus->procdir is in place before any device
> > can be added to the bus.
> > 
> > Therefore, by the time pci_proc_attach_device() runs on these buses,
> > bus->procdir is already set and the racy proc_mkdir() call is never
> > reached.
> > 
> > For buses created before pci_proc_init() sets proc_initialized (the
> > common x86 ACPI case), the bus creation hooks return early.  As such,
> > add a fallback call to pci_proc_attach_bus() from pci_proc_attach_device()
> > to handle these pre-init buses.
> > 
> > Additionally, wrap the for_each_pci_dev() loop in pci_proc_init() with
> > pci_lock_rescan_remove() to serialise against concurrent PCI bus
> > operations, add an early return in pci_proc_attach_device() when
> > dev->procent is already set to make the function idempotent, and clear
> > bus->procdir in pci_proc_detach_bus() to prevent use of a dangling
> > pointer after proc_remove().
> > 
> > Closes: https://lore.kernel.org/linux-pci/20250702155112.40124-2-heshuan@bytedance.com/
> 
> Applied to procfs, as I want this to have some soak time via linux-next,
> plus 0-day bot will test it for me, too.

I will be sending a v4 shortly, which aims to solve this problem with
a different approach as moving procfs directories to the bus creation time
has an unwelcome side effect of leaving empty directories for post-init
creation time, such as remove/rescan or when devices are added via
a hotplug, etc.

Thank you!

	Krzysztof