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

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Message-ID: <c696c21e-97c6-4bfa-bdb4-d519416f5c99@163.com>
Date: Sun, 6 Apr 2025 00:41:31 +0800
From: Hans Zhang <18255117159@....com>
To: Christophe JAILLET <christophe.jaillet@...adoo.fr>
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



On 2025/4/6 00:14, Christophe JAILLET wrote:
> 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?
> 


Hi Christophe,

You're right, and I'm sorry about that.

The following line of code only makes sense if the #if 
defined(CONFIG_PCIEASPM) condition holds. Do we need to optimize this?

pcie->debugfs = debugfs_create_dir(name, NULL);

Best regards,
Hans