linux-kernel - Re: [PATCH] PM: add: move warn message out of mutex lock.

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Message-ID: <2024090212-shuffling-gimmick-a2dc@gregkh>
Date: Mon, 2 Sep 2024 08:31:35 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: David Wang <00107082@....com>
Cc: rafael@...nel.org, len.brown@...el.com, pavel@....cz,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PM: add: move warn message out of mutex lock.

On Mon, Sep 02, 2024 at 01:49:59PM +0800, David Wang wrote:
> dpm_list_mtx does not protect any data used by
> dev_warn for checking parent's power, move
> dev_warn out of mutex lock block make the
> lock more efficient, especially when the warn
> is triggered. This can happen on some HW when
> resume from suspend with USB camera opened:

Please wrap changelog lines at 72 columns if possible.

>  >usb 3-1.1: reset high-speed USB device number 4 using xhci_hcd
>  >..
>  >ep_81: PM: parent 3-1.1:1.1 should not be sleeping
> 
> Signed-off-by: David Wang <00107082@....com>
> ---
>  drivers/base/power/main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> index 4a67e83300e1..934e5bb61f13 100644
> --- a/drivers/base/power/main.c
> +++ b/drivers/base/power/main.c
> @@ -134,10 +134,10 @@ void device_pm_add(struct device *dev)
>  	pr_debug("Adding info for %s:%s\n",
>  		 dev->bus ? dev->bus->name : "No Bus", dev_name(dev));
>  	device_pm_check_callbacks(dev);
> -	mutex_lock(&dpm_list_mtx);
>  	if (dev->parent && dev->parent->power.is_prepared)
>  		dev_warn(dev, "parent %s should not be sleeping\n",
>  			dev_name(dev->parent));
> +	mutex_lock(&dpm_list_mtx);

I do not understand how this change will remove the offending log
message.  It should be safe to hold the lock while the check happens and
the message is printed out, you should not see any functional change at
all.

So are you sure this is needed?

thanks,

greg k-h