Re: [PATCH 0/9] Containers (V9): Generic Process Containers

[Christoph Hellwig <hch@infradead.org>]

On Mon, Apr 30, 2007 at 10:42:25PM +0530, Srivatsa Vaddagiri wrote:
> On Sun, Apr 29, 2007 at 02:37:21AM -0700, Paul Jackson wrote:
> > It builds and boots and mounts the cpuset file system ok.
> > But trying to write the 'mems' file hangs the system hard.
> 
> Basically we are attempting a read_lock(&tasklist_lock) in
> container_task_count() after taking write_lock_irq(&tasklist_lock) in
> update_nodemask()!
> 
> This patch seems to fix the prb for me:
> 
> 
> Fix write_lock() followed by read_lock() bug by introducing a 2nd
> argument to be passed into container_task_count. Other choice is to
> introduce a lock and unlocked versions of container_task_count() ..
> 
> Signed-off-by : Srivatsa Vaddagiri <vatsa@in.ibm.com>

> -int container_task_count(const struct container *cont) {
> +int container_task_count(const struct container *cont, int take_lock) {
>  	int count = 0;
>  	struct task_struct *g, *p;
>  	struct container_subsys_state *css;
>  	int subsys_id;
>  	get_first_subsys(cont, &css, &subsys_id);
>  
> -	read_lock(&tasklist_lock);
> +	if (take_lock)
> +		read_lock(&tasklist_lock);
>  	do_each_thread(g, p) {
>  		if (task_subsys_state(p, subsys_id) == css)
>  			count ++;
>  	} while_each_thread(g, p);
> -	read_unlock(&tasklist_lock);
> +	if (take_lock)
> +		read_unlock(&tasklist_lock);
>  	return count;

Umm, no - please naje two versions with and without the lock.  Also
Please fix up the codingstyle, the { belongs onto a line of it's own.