netdev - Re: [PATCH net] net: page_pool: allow enabling recycling late, fix false positive warning

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Message-ID: <20250801140506.5b3e7213@kernel.org>
Date: Fri, 1 Aug 2025 14:05:06 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Stanislav Fomichev <stfomichev@...il.com>
Cc: davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
 pabeni@...hat.com, andrew+netdev@...n.ch, horms@...nel.org, David Wei
 <dw@...idwei.uk>, michael.chan@...adcom.com, pavan.chebbi@...adcom.com,
 hawk@...nel.org, ilias.apalodimas@...aro.org, almasrymina@...gle.com,
 sdf@...ichev.me
Subject: Re: [PATCH net] net: page_pool: allow enabling recycling late, fix
 false positive warning

On Fri, 1 Aug 2025 13:55:09 -0700 Stanislav Fomichev wrote:
> > +static void bnxt_enable_rx_page_pool(struct bnxt_rx_ring_info *rxr)
> > +{
> > +	page_pool_enable_direct_recycling(rxr->head_pool, &rxr->bnapi->napi);
> > +	page_pool_enable_direct_recycling(rxr->page_pool, &rxr->bnapi->napi);  
> 
> We do bnxt_separate_head_pool check for the disable_direct_recycling
> of head_pool. Is it safe to skip the check here because we always allocate two
> pps from queue_mgmt callbacks? (not clear for me from a quick glance at
> bnxt_alloc_rx_page_pool)

It's safe (I hope) because the helper is duplicate-call-friendly:

+void page_pool_enable_direct_recycling(struct page_pool *pool,
+				       struct napi_struct *napi)
+{
+	if (READ_ONCE(pool->p.napi) == napi)   <<< right here
+		return;
+	WARN_ON_ONCE(!napi || pool->p.napi);
+
+	mutex_lock(&page_pools_lock);
+	WRITE_ONCE(pool->p.napi, napi);
+	mutex_unlock(&page_pools_lock);
+}

We already have a refcount in page pool, I'm planning to add
page_pool_get() in net-next and remove the

	if (bnxt_separate_head_pool)

before page_pool_destroy(), too.