linux-kernel - Re: [PATCH] pci: tegra194: Fix debugfs cleanup for !CONFIG

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Message-ID: <727b55b6-ccba-4498-be95-027a9f67dfa9@wanadoo.fr>
Date: Sat, 5 Apr 2025 18:14:46 +0200
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: 18255117159@....com
Cc: bhelgaas@...gle.com, jonathanh@...dia.com, kw@...ux.com,
 linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
 linux-tegra@...r.kernel.org, lpieralisi@...nel.org,
 manivannan.sadhasivam@...aro.org, robh@...nel.org, thierry.reding@...il.com
Subject: Re: [PATCH] pci: tegra194: Fix debugfs cleanup for !CONFIG_PCIEASPM

Le 05/04/2025 à 16:54, Hans Zhang a écrit :
> When CONFIG_PCIEASPM is disabled, debugfs entries are not created, but
> tegra_pcie_dw_remove() and tegra_pcie_dw_shutdown() unconditionally call
> debugfs_remove_recursive(), leading to potential NULL pointer operations.
> 
> Introduce deinit_debugfs() to wrap debugfs_remove_recursive(), which is
> stubbed for !CONFIG_PCIEASPM. Use this function during removal/shutdown to
> ensure debugfs cleanup only occurs when entries were initialized.
> 
> This prevents kernel warnings and instability when ASPM support is
> disabled.
> 

Could you elaborate?


debugfs_remove_recursive() ends either to:

static inline void debugfs_remove(struct dentry *dentry)
{ }
if CONFIG_DEBUG_FS is not set,

or
to a function which starts with:
	if (IS_ERR_OR_NULL(dentry))
		return;
if it is set.


So what does this new deinit_debugfs() add?


Which NULL pointer are you seeing?
Did you actually manage to trigger it?

CJ



> Signed-off-by: Hans Zhang <18255117159-9Onoh4P/yGk@...lic.gmane.org>
> ---
>   drivers/pci/controller/dwc/pcie-tegra194.c | 13 +++++++++++--
>   1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-tegra194.c b/drivers/pci/controller/dwc/pcie-tegra194.c
> index 5103995cd6c7..d762e733c2d8 100644
> --- a/drivers/pci/controller/dwc/pcie-tegra194.c
> +++ b/drivers/pci/controller/dwc/pcie-tegra194.c
> @@ -716,11 +716,20 @@ static void init_debugfs(struct tegra_pcie_dw *pcie)
>   	debugfs_create_devm_seqfile(pcie->dev, "aspm_state_cnt", pcie->debugfs,
>   				    aspm_state_cnt);
>   }
> +
> +static void deinit_debugfs(struct tegra_pcie_dw *pcie)
> +{
> +	if (!pcie->debugfs)
> +		return;
> +
> +	debugfs_remove_recursive(pcie->debugfs);
> +}
>   #else
>   static inline void disable_aspm_l12(struct tegra_pcie_dw *pcie) { return; }
>   static inline void disable_aspm_l11(struct tegra_pcie_dw *pcie) { return; }
>   static inline void init_host_aspm(struct tegra_pcie_dw *pcie) { return; }
>   static inline void init_debugfs(struct tegra_pcie_dw *pcie) { return; }
> +static inline void deinit_debugfs(struct tegra_pcie_dw *pcie) { return; }
>   #endif
>   
>   static void tegra_pcie_enable_system_interrupts(struct dw_pcie_rp *pp)
> @@ -2289,7 +2298,7 @@ static void tegra_pcie_dw_remove(struct platform_device *pdev)
>   		if (!pcie->link_state)
>   			return;
>   
> -		debugfs_remove_recursive(pcie->debugfs);
> +		deinit_debugfs(pcie->debugfs);
>   		tegra_pcie_deinit_controller(pcie);
>   		pm_runtime_put_sync(pcie->dev);
>   	} else {
> @@ -2408,7 +2417,7 @@ static void tegra_pcie_dw_shutdown(struct platform_device *pdev)
>   		if (!pcie->link_state)
>   			return;
>   
> -		debugfs_remove_recursive(pcie->debugfs);
> +		deinit_debugfs(pcie->debugfs);
>   		tegra_pcie_downstream_dev_to_D0(pcie);
>   
>   		disable_irq(pcie->pci.pp.irq);
> 
> base-commit: a8662bcd2ff152bfbc751cab20f33053d74d0963