linux-kernel - Re: [PATCH v2] PCI: take the rescan lock when adding devices during host probe

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Message-ID: <20241003085042.w7d3h2tiogr56un7@thinkpad>
Date: Thu, 3 Oct 2024 14:20:42 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Bartosz Golaszewski <brgl@...ev.pl>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
	Konrad Dybcio <konradybcio@...nel.org>
Subject: Re: [PATCH v2] PCI: take the rescan lock when adding devices during
 host probe

On Thu, Oct 03, 2024 at 10:43:41AM +0200, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> 
> Since adding the PCI power control code, we may end up with a race
> between the pwrctl platform device rescanning the bus and the host
> controller probe function. The latter needs to take the rescan lock when
> adding devices or we may end up in an undefined state having two
> incompletely added devices and hit the following crash when trying to
> remove the device over sysfs:
> 
> Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
> Internal error: Oops: 0000000096000004 [#1] SMP
> Call trace:
>   __pi_strlen+0x14/0x150
>   kernfs_find_ns+0x80/0x13c
>   kernfs_remove_by_name_ns+0x54/0xf0
>   sysfs_remove_bin_file+0x24/0x34
>   pci_remove_resource_files+0x3c/0x84
>   pci_remove_sysfs_dev_files+0x28/0x38
>   pci_stop_bus_device+0x8c/0xd8
>   pci_stop_bus_device+0x40/0xd8
>   pci_stop_and_remove_bus_device_locked+0x28/0x48
>   remove_store+0x70/0xb0
>   dev_attr_store+0x20/0x38
>   sysfs_kf_write+0x58/0x78
>   kernfs_fop_write_iter+0xe8/0x184
>   vfs_write+0x2dc/0x308
>   ksys_write+0x7c/0xec
> 

Thanks for adding the crash log. It always helps to have the log in patch
description to find *this* patch.

> Reported-by: Konrad Dybcio <konradybcio@...nel.org>
> Tested-by: Konrad Dybcio <konradybcio@...nel.org>
> Fixes: 4565d2652a37 ("PCI/pwrctl: Add PCI power control core code")
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>

Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>

- Mani

> ---
> v1 -> v2:
> - improve the commit message, add example stack trace
> 
>  drivers/pci/probe.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 4f68414c3086..f1615805f5b0 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -3105,7 +3105,9 @@ int pci_host_probe(struct pci_host_bridge *bridge)
>  	list_for_each_entry(child, &bus->children, node)
>  		pcie_bus_configure_settings(child);
>  
> +	pci_lock_rescan_remove();
>  	pci_bus_add_devices(bus);
> +	pci_unlock_rescan_remove();
>  	return 0;
>  }
>  EXPORT_SYMBOL_GPL(pci_host_probe);
> -- 
> 2.30.2
> 
> 

-- 
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