Re: [PATCH v4 net-next 1/4] net: core: page_pool: add user cnt preventing pool deletion

[Ivan Khoronzhuk]

On Tue, Jun 25, 2019 at 09:36:15PM -0400, Willem de Bruijn wrote:
> On Tue, Jun 25, 2019 at 2:00 PM Ivan Khoronzhuk
> <ivan.khoronzhuk@xxxxxxxxxx> wrote:
> > Add user counter allowing to delete pool only when no users.
> > It doesn't prevent pool from flush, only prevents freeing the
> > pool instance. Helps when no need to delete the pool and now
> > it's user responsibility to free it by calling page_pool_free()
> > while destroying procedure. It also makes to use page_pool_free()
> > explicitly, not fully hidden in xdp unreg, which looks more
> > correct after page pool "create" routine.
> >
> > Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@xxxxxxxxxx>
> > ---
>
> > diff --git a/include/net/page_pool.h b/include/net/page_pool.h
> > index f07c518ef8a5..1ec838e9927e 100644
> > --- a/include/net/page_pool.h
> > +++ b/include/net/page_pool.h
> > @@ -101,6 +101,7 @@ struct page_pool {
> >         struct ptr_ring ring;
> >
> >         atomic_t pages_state_release_cnt;
> > +       atomic_t user_cnt;
>
> refcount_t?
yes, thanks.

> >  };
> >
> >  struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp);
> > @@ -183,6 +184,12 @@ static inline dma_addr_t page_pool_get_dma_addr(struct page *page)
> >         return page->dma_addr;
> >  }
> >
> > +/* used to prevent pool from deallocation */
> > +static inline void page_pool_get(struct page_pool *pool)
> > +{
> > +       atomic_inc(&pool->user_cnt);
> > +}
> > +
> >  static inline bool is_page_pool_compiled_in(void)
> >  {
> >  #ifdef CONFIG_PAGE_POOL
> > diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> > index b366f59885c1..169b0e3c870e 100644
> > --- a/net/core/page_pool.c
> > +++ b/net/core/page_pool.c
> > @@ -48,6 +48,7 @@ static int page_pool_init(struct page_pool *pool,
> >                 return -ENOMEM;
> >
> >         atomic_set(&pool->pages_state_release_cnt, 0);
> > +       atomic_set(&pool->user_cnt, 0);
> >
> >         if (pool->p.flags & PP_FLAG_DMA_MAP)
> >                 get_device(pool->p.dev);
> > @@ -70,6 +71,8 @@ struct page_pool *page_pool_create(const struct page_pool_params *params)
> >                 kfree(pool);
> >                 return ERR_PTR(err);
> >         }
> > +
> > +       page_pool_get(pool);
> >         return pool;
> >  }
> >  EXPORT_SYMBOL(page_pool_create);
> > @@ -356,6 +359,10 @@ static void __warn_in_flight(struct page_pool *pool)
> >
> >  void __page_pool_free(struct page_pool *pool)
> >  {
> > +       /* free only if no users */
> > +       if (!atomic_dec_and_test(&pool->user_cnt))
> > +               return;
> > +
> >         WARN(pool->alloc.count, "API usage violation");
> >         WARN(!ptr_ring_empty(&pool->ring), "ptr_ring is not empty");
> >
> > diff --git a/net/core/xdp.c b/net/core/xdp.c
> > index 829377cc83db..04bdcd784d2e 100644
> > --- a/net/core/xdp.c
> > +++ b/net/core/xdp.c
> > @@ -372,6 +372,9 @@ int xdp_rxq_info_reg_mem_model(struct xdp_rxq_info *xdp_rxq,
> >
> >         mutex_unlock(&mem_id_lock);
> >
> > +       if (type == MEM_TYPE_PAGE_POOL)
> > +               page_pool_get(xdp_alloc->page_pool);
> > +
>
> need an analogous page_pool_put in xdp_rxq_info_unreg_mem_model? mlx5
> does not use that inverse function, but intel drivers do.
no need, it's put after call to page_pool_free() in unreg workqueue.

> >         trace_mem_connect(xdp_alloc, xdp_rxq);
> >         return 0;
> >  err:
> > --
> > 2.17.1

--
Regards,
Ivan Khoronzhuk