staging: comedi: comedi_fops: do not call blocking ops when !TASK_RUNNING

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@rsyncme.org>
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Cc: <stable@vger.kernel.org> # 4.5+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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;