xdp: force mem allocator removal and periodic warning

If bugs exists or are introduced later e.g. by drivers misusing the API,
then we want to warn about the issue, such that developer notice. This patch
will generate a bit of noise in form of periodic pr_warn every 30 seconds.

It is not nice to have this stall warning running forever. Thus, this patch
will (after 120 attempts) force disconnect the mem id (from the rhashtable)
and free the page_pool object. This will cause fallback to the put_page() as
before, which only potentially leak DMA-mappings, if objects are really
stuck for this long. In that unlikely case, a WARN_ONCE should show us the
call stack.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 17 insertions, 1 deletions

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 8679e24fd665..42c3b0a5a259 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -330,11 +330,27 @@ static void __page_pool_empty_ring(struct page_pool *pool)
 	}
 }
 
+static void __warn_in_flight(struct page_pool *pool)
+{
+	u32 release_cnt = atomic_read(&pool->pages_state_release_cnt);
+	u32 hold_cnt = READ_ONCE(pool->pages_state_hold_cnt);
+	s32 distance;
+
+	distance = _distance(hold_cnt, release_cnt);
+
+	/* Drivers should fix this, but only problematic when DMA is used */
+	WARN(1, "Still in-flight pages:%d hold:%u released:%u",
+	     distance, hold_cnt, release_cnt);
+}
+
 void __page_pool_free(struct page_pool *pool)
 {
 	WARN(pool->alloc.count, "API usage violation");
 	WARN(!ptr_ring_empty(&pool->ring), "ptr_ring is not empty");
-	WARN(!__page_pool_safe_to_destroy(pool), "still in-flight pages");
+
+	/* Can happen due to forced shutdown */
+	if (!__page_pool_safe_to_destroy(pool))
+		__warn_in_flight(pool);
 
 	ptr_ring_cleanup(&pool->ring, NULL);
 	kfree(pool);