[PATCH v6 net-next 1/5] xdp: allow same allocator usage

[Ivan Khoronzhuk]

First of all, it is an absolute requirement that each RX-queue have
their own page_pool object/allocator. And this change is intendant
to handle special case, where a single RX-queue can receive packets
from two different net_devices.

In order to protect against using same allocator for 2 different rx
queues, add queue_index to xdp_mem_allocator to catch the obvious
mistake where queue_index mismatch, as proposed by Jesper Dangaard
Brouer.

Adding this on xdp allocator level allows drivers with such dependency
change the allocators w/o modifications.

Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@xxxxxxxxxx>
---
 include/net/xdp_priv.h |  2 ++
 net/core/xdp.c         | 55 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 57 insertions(+)

diff --git a/include/net/xdp_priv.h b/include/net/xdp_priv.h
index 6a8cba6ea79a..9858a4057842 100644
--- a/include/net/xdp_priv.h
+++ b/include/net/xdp_priv.h
@@ -18,6 +18,8 @@ struct xdp_mem_allocator {
 	struct rcu_head rcu;
 	struct delayed_work defer_wq;
 	unsigned long defer_warn;
+	unsigned long refcnt;
+	u32 queue_index;
 };
 
 #endif /* __LINUX_NET_XDP_PRIV_H__ */
diff --git a/net/core/xdp.c b/net/core/xdp.c
index 829377cc83db..4f0ddbb3717a 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -98,6 +98,18 @@ static bool __mem_id_disconnect(int id, bool force)
 		WARN(1, "Request remove non-existing id(%d), driver bug?", id);
 		return true;
 	}
+
+	/* to avoid calling hash lookup twice, decrement refcnt here till it
+	 * reaches zero, then it can be called from workqueue afterwards.
+	 */
+	if (xa->refcnt)
+		xa->refcnt--;
+
+	if (xa->refcnt) {
+		mutex_unlock(&mem_id_lock);
+		return true;
+	}
+
 	xa->disconnect_cnt++;
 
 	/* Detects in-flight packet-pages for page_pool */
@@ -312,6 +324,33 @@ static bool __is_supported_mem_type(enum xdp_mem_type type)
 	return true;
 }
 
+static struct xdp_mem_allocator *xdp_allocator_find(void *allocator)
+{
+	struct xdp_mem_allocator *xae, *xa = NULL;
+	struct rhashtable_iter iter;
+
+	if (!allocator)
+		return xa;
+
+	rhashtable_walk_enter(mem_id_ht, &iter);
+	do {
+		rhashtable_walk_start(&iter);
+
+		while ((xae = rhashtable_walk_next(&iter)) && !IS_ERR(xae)) {
+			if (xae->allocator == allocator) {
+				xa = xae;
+				break;
+			}
+		}
+
+		rhashtable_walk_stop(&iter);
+
+	} while (xae == ERR_PTR(-EAGAIN));
+	rhashtable_walk_exit(&iter);
+
+	return xa;
+}
+
 int xdp_rxq_info_reg_mem_model(struct xdp_rxq_info *xdp_rxq,
 			       enum xdp_mem_type type, void *allocator)
 {
@@ -347,6 +386,20 @@ int xdp_rxq_info_reg_mem_model(struct xdp_rxq_info *xdp_rxq,
 		}
 	}
 
+	mutex_lock(&mem_id_lock);
+	xdp_alloc = xdp_allocator_find(allocator);
+	if (xdp_alloc) {
+		/* One allocator per queue is supposed only */
+		if (xdp_alloc->queue_index != xdp_rxq->queue_index)
+			return -EINVAL;
+
+		xdp_rxq->mem.id = xdp_alloc->mem.id;
+		xdp_alloc->refcnt++;
+		mutex_unlock(&mem_id_lock);
+		return 0;
+	}
+	mutex_unlock(&mem_id_lock);
+
 	xdp_alloc = kzalloc(sizeof(*xdp_alloc), gfp);
 	if (!xdp_alloc)
 		return -ENOMEM;
@@ -360,6 +413,8 @@ int xdp_rxq_info_reg_mem_model(struct xdp_rxq_info *xdp_rxq,
 	xdp_rxq->mem.id = id;
 	xdp_alloc->mem  = xdp_rxq->mem;
 	xdp_alloc->allocator = allocator;
+	xdp_alloc->refcnt = 1;
+	xdp_alloc->queue_index = xdp_rxq->queue_index;
 
 	/* Insert allocator into ID lookup table */
 	ptr = rhashtable_insert_slow(mem_id_ht, &id, &xdp_alloc->node);
-- 
2.17.1