linux-kernel - [RFC 0/1] PCI: Fix pci devices double register WARNING in the kernel starting process

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Message-Id: <20250702155112.40124-1-heshuan@bytedance.com>
Date: Wed,  2 Jul 2025 23:51:11 +0800
From: Shuan He <heshuan@...edance.com>
To: bhelgaas@...gle.com,
	cuiyunhui@...edance.com
Cc: linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	heshuan@...edance.com,
	sunilvl@...tanamicro.com
Subject: [RFC 0/1] PCI: Fix pci devices double register WARNING in the kernel starting process

Hi All.
I encountered a WARNING printed out during the kernel starting process
on my developing environment.
(with RISC-V arch, 6.12 kernel, and Debian 13 OS).

WARN Trace:
[    0.518993] proc_dir_entry '000c:00/00.0' already registered
[    0.519187] WARNING: CPU: 2 PID: 179 at fs/proc/generic.c:375 proc_register+0xf6/0x180
[    0.519214] [<ffffffff804055a6>] proc_register+0xf6/0x180
[    0.519217] [<ffffffff80405a9e>] proc_create_data+0x3e/0x60
[    0.519220] [<ffffffff80616e44>] pci_proc_attach_device+0x74/0x130
[    0.509991] [<ffffffff805f1af2>] pci_bus_add_device+0x42/0x100
[    0.509997] [<ffffffff805f1c76>] pci_bus_add_devices+0xc6/0x110
[    0.519230] [<ffffffff8066763c>] acpi_pci_root_add+0x54c/0x810
[    0.519233] [<ffffffff8065d206>] acpi_bus_attach+0x196/0x2f0
[    0.519234] [<ffffffff8065d390>] acpi_scan_clear_dep_fn+0x30/0x70
[    0.519236] [<ffffffff800468fa>] process_one_work+0x19a/0x390
[    0.519239] [<ffffffff80047a6e>] worker_thread+0x2be/0x420
[    0.519241] [<ffffffff80050dc4>] kthread+0xc4/0xf0
[    0.519243] [<ffffffff80ad6ad2>] ret_from_fork+0xe/0x1c

After digging into this issue a little bit, I find the double-register
of PCIe devices occurs in the following logic:

Early:
static int __init pci_proc_init(void)
{
...
    for_each_pci_dev(dev)
        pci_proc_attach_device(dev);
        //000c:00:00.0 will be registered here for the first time (succeeded).
...
}

Later:
acpi_pci_root_add
-> pci_bus_add_devices
  -> pci_bus_add_device
    -> pci_proc_attach_device
    //try to register 000c:00:00.0 here for the second time
      (failed and triggered the WARNING trace);

I tried to add two more steps in the pci_proc_init function
(shown in the attached patch).
1st is to prevent the concurrent issue by holding the
pci_rescan_remove_lock.
2nd is to correctly update the device's status after
it's been successfully registered (by adding the
PCI_DEV_ADDED bit to the device's flag).

Then the WARNING disappeared and the system worked well. 

I understand that the device_initcall(pci_proc_init) function
stays there already for 20 years (time of the initiliaztion of
repo), and it hasn't really changed since then.
So I wonder if my patch is the RIGHT way to fix this WARNING issue?
I am not positive about this. :(

Any suggestions?

As a beginner Linux programmer, I am not sure whether I have included
all related reviews/maintainers in my email list, but sincerely seeking
your help and any comments are very welcome.

Warmly regards,
Shuan

Shuan He (1):
  PCI: Fix pci devices double register WARN in the kernel starting
    process

 drivers/pci/proc.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

-- 
2.39.5 (Apple Git-154)