[Devel] Re: [PATCH] Check for error returned by kthread_create on creating journal thread

[Christoph Hellwig]

On Mon, Apr 16, 2007 at 11:41:14AM +0400, Pavel Emelianov wrote:
> If the thread failed to create the subsequent wait_event
> will hang forever.
> 
> This is likely to happen if kernel hits max_threads limit.
> 
> Will be critical for virtualization systems that limit the
> number of tasks and kernel memory usage within the container.

> --- ./fs/jbd/journal.c.jbdthreads	2007-04-16 11:17:36.000000000 +0400
> +++ ./fs/jbd/journal.c	2007-04-16 11:30:09.000000000 +0400
> @@ -211,10 +211,16 @@ end_loop:
>  	return 0;
>  }
>  
> -static void journal_start_thread(journal_t *journal)
> +static int journal_start_thread(journal_t *journal)
>  {
> -	kthread_run(kjournald, journal, "kjournald");
> +	struct task_struct *t;
> +
> +	t = kthread_run(kjournald, journal, "kjournald");
> +	if (IS_ERR(t))
> +		return PTR_ERR(t);
> +
>  	wait_event(journal->j_wait_done_commit, journal->j_task != 0);

Note that this wait_event should exist at all, and the return
value of kthread_run should be assigned to journal->j_task.  Also
the code doesn't use the kthread primitives in other places leading
to crufty code.