linux-kernel - Re: [PATCH] staging: comedi: comedi_fops: do not call blocking ops when !TASK

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Date:   Tue, 1 Aug 2017 08:23:29 +0100
From:   Piotr Gregor <piotrgregor@...ncme.org>
To:     Ian Abbott <abbotti@....co.uk>
Cc:     devel@...verdev.osuosl.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        H Hartley Sweeten <hsweeten@...ionengravers.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] staging: comedi: comedi_fops: do not call blocking ops
 when !TASK_RUNNING

On Fri, Jul 28, 2017 at 04:22:31PM +0100, Ian Abbott wrote:
> Comedi's read and write file operation handlers (`comedi_read()` and
> `comedi_write()`) currently call `copy_to_user()` or `copy_from_user()`
> whilst in the `TASK_INTERRUPTIBLE` state, which falls foul of the
> `might_fault()` checks when enabled.  Fix it by setting the current task
> state back to `TASK_RUNNING` a bit earlier before calling these
> functions.
> 
> Reported-by: Piotr Gregor <piotrgregor@...ncme.org>
> Signed-off-by: Ian Abbott <abbotti@....co.uk>
> Cc: <stable@...r.kernel.org> # 4.5+
> ---
> Note: stable kernel versions 4.4 and earlier will need a slightly more
> extensive change in `comedi_write()` than provided by this patch due to
> a call to `mutex_lock()` whilst in the `TASK_INTERRUPTIBLE` state.
> ---
>  drivers/staging/comedi/comedi_fops.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
> index ca11be21f64b..34ca7823255d 100644
> --- a/drivers/staging/comedi/comedi_fops.c
> +++ b/drivers/staging/comedi/comedi_fops.c
> @@ -2396,6 +2396,7 @@ static ssize_t comedi_write(struct file *file, const char __user *buf,
>  			continue;
>  		}
>  
> +		set_current_state(TASK_RUNNING);
>  		wp = async->buf_write_ptr;
>  		n1 = min(n, async->prealloc_bufsz - wp);
>  		n2 = n - n1;
> @@ -2528,6 +2529,8 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes,
>  			}
>  			continue;
>  		}
> +
> +		set_current_state(TASK_RUNNING);
>  		rp = async->buf_read_ptr;
>  		n1 = min(n, async->prealloc_bufsz - rp);
>  		n2 = n - n1;
> -- 
> 2.13.2
> 

Hi Ian,

I will be able to test this in a couple of days.

cheers,
Piotr