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Date:   Wed, 9 Jun 2021 11:47:15 -0700
From:   Jack Pham <jackp@codeaurora.org>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
        Felipe Balbi <balbi@kernel.org>,
        Peter Chen <peter.chen@kernel.org>
Subject: Re: [PATCH] USB: dwc3: remove debugfs root dentry storage
Message-ID: <20210609184715.GA28957@jackp-linux.qualcomm.com>
References: <20210609093924.3293230-1-gregkh@linuxfoundation.org>
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On Wed, Jun 09, 2021 at 11:39:24AM +0200, Greg Kroah-Hartman wrote:
> There is no need to keep around the debugfs "root" directory for the
> dwc3 device.  Instead, look it up anytime we need to find it.  This will
> help when callers get out-of-order and we had the potential to have a
> "stale" pointer around for the root dentry, as has happened in the past.
> 
> Cc: Felipe Balbi <balbi@kernel.org>
> Cc: Jack Pham <jackp@codeaurora.org>
> Cc: Peter Chen <peter.chen@kernel.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>  drivers/usb/dwc3/core.h    | 2 --
>  drivers/usb/dwc3/debugfs.c | 8 ++++----
>  drivers/usb/dwc3/gadget.c  | 4 +++-
>  3 files changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
> index c5d5760cdf53..dccdf13b5f9e 100644
> --- a/drivers/usb/dwc3/core.h
> +++ b/drivers/usb/dwc3/core.h
> @@ -1013,7 +1013,6 @@ struct dwc3_scratchpad_array {
>   * @link_state: link state
>   * @speed: device speed (super, high, full, low)
>   * @hwparams: copy of hwparams registers
> - * @root: debugfs root folder pointer
>   * @regset: debugfs pointer to regdump file
>   * @dbg_lsp_select: current debug lsp mux register selection
>   * @test_mode: true when we're entering a USB test mode
> @@ -1222,7 +1221,6 @@ struct dwc3 {
>  	u8			num_eps;
>  
>  	struct dwc3_hwparams	hwparams;
> -	struct dentry		*root;
>  	struct debugfs_regset32	*regset;
>  
>  	u32			dbg_lsp_select;
> diff --git a/drivers/usb/dwc3/debugfs.c b/drivers/usb/dwc3/debugfs.c
> index 5dbbe53269d3..f2b7675c7f62 100644
> --- a/drivers/usb/dwc3/debugfs.c
> +++ b/drivers/usb/dwc3/debugfs.c
> @@ -889,8 +889,10 @@ static void dwc3_debugfs_create_endpoint_files(struct dwc3_ep *dep,
>  void dwc3_debugfs_create_endpoint_dir(struct dwc3_ep *dep)
>  {
>  	struct dentry		*dir;
> +	struct dentry		*root;
>  
> -	dir = debugfs_create_dir(dep->name, dep->dwc->root);
> +	root = debugfs_lookup(dev_name(dep->dwc->dev), usb_debug_root);
> +	dir = debugfs_create_dir(dep->name, root);
>  	dwc3_debugfs_create_endpoint_files(dep, dir);
>  }
>  
> @@ -909,8 +911,6 @@ void dwc3_debugfs_init(struct dwc3 *dwc)
>  	dwc->regset->base = dwc->regs - DWC3_GLOBALS_REGS_START;
>  
>  	root = debugfs_create_dir(dev_name(dwc->dev), usb_debug_root);
> -	dwc->root = root;
> -
>  	debugfs_create_regset32("regdump", 0444, root, dwc->regset);
>  	debugfs_create_file("lsp_dump", 0644, root, dwc, &dwc3_lsp_fops);
>  
> @@ -929,6 +929,6 @@ void dwc3_debugfs_init(struct dwc3 *dwc)
>  
>  void dwc3_debugfs_exit(struct dwc3 *dwc)
>  {
> -	debugfs_remove_recursive(dwc->root);
> +	debugfs_remove(debugfs_lookup(dev_name(dwc->dev), usb_debug_root));
>  	kfree(dwc->regset);
>  }
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index 7cc99b6d0bfe..026a2ad0fc80 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -2799,7 +2799,9 @@ static void dwc3_gadget_free_endpoints(struct dwc3 *dwc)
>  			list_del(&dep->endpoint.ep_list);
>  		}
>  
> -		debugfs_remove_recursive(debugfs_lookup(dep->name, dwc->root));
> +		debugfs_remove_recursive(debugfs_lookup(dep->name,
> +				debugfs_lookup(dev_name(dep->dwc->dev),
> +					       usb_debug_root)));

Nested calls to debugfs_lookup() :). But it does work, and similarly
avoids the out-of-order debugfs removal issue as well even without
Peter's fix.

Tested-by: Jack Pham <jackp@codeaurora.org>

Thanks
Jack
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