[CRIU] Re: [PATCH cr 5/6] pstree: allocate rst parts from a shared region

[Andrew Vagin]

On Tue, Oct 02, 2012 at 07:58:02PM +0400, Pavel Emelyanov wrote:
> On 10/02/2012 06:07 PM, Andrey Vagin wrote:
> > The next patch will add a futex, which will be used for restoring
> > shared fd tables.
> > 
> > Signed-off-by: Andrey Vagin <avagin at openvz.org>
> > ---
> >  include/pstree.h |    2 +-
> >  pstree.c         |    8 +++++++-
> >  2 files changed, 8 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/pstree.h b/include/pstree.h
> > index 0790b49..2da7176 100644
> > --- a/include/pstree.h
> > +++ b/include/pstree.h
> > @@ -20,7 +20,7 @@ struct pstree_item {
> >  	int			state;		/* TASK_XXX constants */
> >  	int			nr_threads;	/* number of threads */
> >  	struct pid		*threads;	/* array of threads */
> > -	struct rst_info		rst[0];
> > +	struct rst_info		*rst;
> >  };
> >  
> >  extern void free_pstree(struct pstree_item *root_item);
> > diff --git a/pstree.c b/pstree.c
> > index 8df5a63..1672b26 100644
> > --- a/pstree.c
> > +++ b/pstree.c
> > @@ -33,10 +33,16 @@ struct pstree_item *__alloc_pstree_item(bool rst)
> >  {
> >  	struct pstree_item *item;
> >  
> > -	item = xzalloc(sizeof(*item) + (rst ? sizeof(item->rst[0]) : 0));
> > +	item = xzalloc(sizeof(*item));
> >  	if (!item)
> >  		return NULL;
> >  
> > +	if (rst) {
> > +		item->rst = shmalloc(sizeof(item->rst[0]));
> 
> The smalloc has caveat -- it's hared with children _only_. Does that suit us?
Yes, because all pstree items are allocated in crtools before retoring
a root task.
> Thing #2. The rst_info is generic rst_info, what if we add there something which
> is not fdtable related? Things will get broken.
I don't understand this point. Here are a few list heads already. Now
rst_info is used only by owner and only fdt_lock can be used by another
task, so we don't have problem.
> 
> > +		if (!item->rst)
> > +			return NULL;
> > +	}
> > +
> >  	INIT_LIST_HEAD(&item->children);
> >  	item->threads = NULL;
> >  	item->nr_threads = 0;
> > 
> 
>