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Re: [Cluster-devel] [PATCH] [GFS2] bz 276631 : GFS2: chmod hung - TRY 2



On Thu, Sep 13, 2007 at 11:04:43PM -0500, Bob Peterson wrote:
> diff -pur a/fs/gfs2/locking/dlm/thread.c b/fs/gfs2/locking/dlm/thread.c
> --- a/fs/gfs2/locking/dlm/thread.c	2007-09-13 17:33:58.000000000 -0500
> +++ b/fs/gfs2/locking/dlm/thread.c	2007-09-13 22:47:14.000000000 -0500
> @@ -279,8 +279,10 @@ static int gdlm_thread(void *data)
>  	/* Only thread1 is allowed to do blocking callbacks since gfs
>  	   may wait for a completion callback within a blocking cb. */
>  
> +	spin_lock(&ls->async_lock);
>  	if (current == ls->thread1)
>  		blist = 1;
> +	spin_unlock(&ls->async_lock);
>  
>  	while (!kthread_should_stop()) {
>  		set_current_state(TASK_INTERRUPTIBLE);
> @@ -338,10 +340,12 @@ int gdlm_init_threads(struct gdlm_ls *ls
>  	struct task_struct *p;
>  	int error;
>  
> +	spin_lock(&ls->async_lock);
>  	p = kthread_run(gdlm_thread, ls, "lock_dlm1");
>  	error = IS_ERR(p);
>  	if (error) {
>  		log_error("can't start lock_dlm1 thread %d", error);
> +		spin_unlock(&ls->async_lock);
>  		return error;
>  	}
>  	ls->thread1 = p;
> @@ -351,9 +355,11 @@ int gdlm_init_threads(struct gdlm_ls *ls
>  	if (error) {
>  		log_error("can't start lock_dlm2 thread %d", error);
>  		kthread_stop(ls->thread1);
> +		spin_unlock(&ls->async_lock);
>  		return error;
>  	}
>  	ls->thread2 = p;
> +	spin_unlock(&ls->async_lock);

This is strange.  First, it seems very likely to me that kthread_run could
sleep, and almost certain that kthread_stop will sleep.  Second, using a
spinlock to signal a completion from one thread to another like this may
be common with mutexes/completions, but not with spinlocks.  I'd suggest
one of two alternatives.  Either have the thread check it's own name for
"lock_dlm1", or add a new gdlm_thread1 function, i.e.

int _gdlm_thread(struct gdlm_ls *ls, int blist)
{
	/* current function goes here */
}

int gdlm_thread1(void *data)
{
	return _gdlm_thread(data, 1);
}

int gdlm_thread2(void *data)
{
	return _gdlm_thread(data, 0);
}

kthread_run(gdlm_thread1, ls, "lock_dlm1");
kthread_run(gdlm_thread2, ls, "lock_dlm2");


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