Re: [PATCH 5/6] kmod: Add new call_usermodehelper_timeout() API

[Oleg Nesterov <oleg@redhat.com>]

Hi Boaz,

I'll read this series tomorrow, but

On 03/26, Boaz Harrosh wrote:
>
>  int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
>  {
>  	DECLARE_COMPLETION_ONSTACK(done);
> +	int wait_state;
>  	int retval = 0;
>
>  	helper_lock();
> @@ -540,19 +541,15 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
>  	if (wait == UMH_NO_WAIT)	/* task has freed sub_info */
>  		goto unlock;
>
> -	if (wait & UMH_KILLABLE) {
> -		retval = wait_for_completion_killable(&done);
> -		if (!retval)
> -			goto wait_done;
> -
> +	wait_state = (wait & UMH_KILLABLE) ? TASK_KILLABLE : 0;
> +	retval = wait_for_completion_timeout_state(&done, sub_info->timeout,
> +						   wait_state);
> +	if (unlikely(retval)) {
>  		/* umh_complete() will see NULL and free sub_info */
>  		if (xchg(&sub_info->complete, NULL))
>  			goto unlock;
> -		/* fallthrough, umh_complete() was already called */
>  	}
>
> -	wait_for_completion(&done);

at first glance this looks certainly wrong, or I misread the patch.

We can't remove the "fallback to wait_for_completion" logic until
you move the completion into subprocess_info (the next patch seems
to do this).

xchg() can race with umh_complete(). If it returns NULL, umh_complete()
was already called and got ->complete != NULL, we must not return until
umh_complete() finishes complete().

Oleg.