linux-kernel - Re: [PATCH] platform/surface: dtx: Fix poll function

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Date:   Wed, 19 May 2021 15:12:03 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Maximilian Luz <luzmaximilian@...il.com>
Cc:     Mark Gross <mgross@...ux.intel.com>,
        platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] platform/surface: dtx: Fix poll function

Hi,

On 5/13/21 3:44 PM, Maximilian Luz wrote:
> The poll function should not return -ERESTARTSYS.
> 
> Furthermore, locking in this function is completely unnecessary. The
> ddev->lock protects access to the main device and controller (ddev->dev
> and ddev->ctrl), ensuring that both are and remain valid while being
> accessed by clients. Both are, however, never accessed in the poll
> function. The shutdown test (via atomic bit flags) be safely done
> without locking, so drop locking here entirely.
> 
> Reported-by: kernel test robot <lkp@...el.com>
> Fixes: 1d609992832e ("platform/surface: Add DTX driver> Signed-off-by: Maximilian Luz <luzmaximilian@...il.com>

Thank you for your patch, I've applied this patch to my review-hans 
branch:
https://git.kernel.org/pub/scm/linux/kernel/git/pdx86/platform-drivers-x86.git/log/?h=review-hans

I will also include this in the next pdx86-fixes pull-req for 5.13.

Note it will show up in my review-hans branch once I've pushed my
local branch there, which might take a while.

Once I've run some tests on this branch the patches there will be
added to the platform-drivers-x86/for-next branch and eventually
will be included in the pdx86 pull-request to Linus for the next
merge-window.

Regards,

Hans

> ---
>  drivers/platform/surface/surface_dtx.c | 8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)
> 
> diff --git a/drivers/platform/surface/surface_dtx.c b/drivers/platform/surface/surface_dtx.c
> index 63ce587e79e3..5d9b758a99bb 100644
> --- a/drivers/platform/surface/surface_dtx.c
> +++ b/drivers/platform/surface/surface_dtx.c
> @@ -527,20 +527,14 @@ static __poll_t surface_dtx_poll(struct file *file, struct poll_table_struct *pt
>  	struct sdtx_client *client = file->private_data;
>  	__poll_t events = 0;
>  
> -	if (down_read_killable(&client->ddev->lock))
> -		return -ERESTARTSYS;
> -
> -	if (test_bit(SDTX_DEVICE_SHUTDOWN_BIT, &client->ddev->flags)) {
> -		up_read(&client->ddev->lock);
> +	if (test_bit(SDTX_DEVICE_SHUTDOWN_BIT, &client->ddev->flags))
>  		return EPOLLHUP | EPOLLERR;
> -	}
>  
>  	poll_wait(file, &client->ddev->waitq, pt);
>  
>  	if (!kfifo_is_empty(&client->buffer))
>  		events |= EPOLLIN | EPOLLRDNORM;
>  
> -	up_read(&client->ddev->lock);
>  	return events;
>  }
>  
>