netdev - Re: [PATCH net-next v1 09/11] xdp: force mem allocator removal and periodic warning

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Message-ID: <20190618103706.01fa6fa4@carbon>
Date:   Tue, 18 Jun 2019 10:37:06 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>
Cc:     netdev@...r.kernel.org,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Toke Høiland-Jørgensen <toke@...e.dk>,
        Tariq Toukan <tariqt@...lanox.com>, toshiaki.makita1@...il.com,
        grygorii.strashko@...com, mcroce@...hat.com, brouer@...hat.com
Subject: Re: [PATCH net-next v1 09/11] xdp: force mem allocator removal and
 periodic warning

On Sat, 15 Jun 2019 11:59:16 +0300
Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org> wrote:

> >@@ -388,10 +411,12 @@ static void __xdp_return(void *data, struct xdp_mem_info *mem, bool napi_direct,
> > 		/* mem->id is valid, checked in xdp_rxq_info_reg_mem_model() */
> > 		xa = rhashtable_lookup(mem_id_ht, &mem->id, mem_id_rht_params);
> > 		page = virt_to_head_page(data);
> >-		if (xa) {
> >+		if (likely(xa)) {
> > 			napi_direct &= !xdp_return_frame_no_direct();
> > 			page_pool_put_page(xa->page_pool, page, napi_direct);
>
> Interesting if it's synced with device "unregistration".
> I mean page dma unmap is bind to device that doesn't exist anymore but pages
> from pool of the device are in flight, so pool is not destroyed but what about
> device?. smth like device unreq todo list. Just to be sure, is it synched?

I looked through the code, and you are right.  We are actually missing
to hold a reference count on struct device (for which we use dev->dma_ops).
It looks like we can simply do a get_device() and put_device(). Thus,
fairly simple to fix.

I'll add this fix as a separate patch, as it is a separate issue/bug
that also needs correction... Thanks for catching this!

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer