page_pool: add destroy attempts counter and rename tracepoint

When Jonathan change the page_pool to become responsible to its
own shutdown via deferred work queue, then the disconnect_cnt
counter was removed from xdp memory model tracepoint.

This patch change the page_pool_inflight tracepoint name to
page_pool_release, because it reflects the new responsability
better.  And it reintroduces a counter that reflect the number of
times page_pool_release have been tried.

The counter is also used by the code, to only empty the alloc
cache once.  With a stuck work queue running every second and
counter being 64-bit, it will overrun in approx 584 billion
years. For comparison, Earth lifetime expectancy is 7.5 billion
years, before the Sun will engulf, and destroy, the Earth.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/page_pool.h

@@ -112,6 +112,8 @@ struct page_pool {
 	 * refcnt serves purpose is to simplify drivers error handling.
 	 */
 	refcount_t user_cnt;
+
+	u64 destroy_cnt;
 };
 
 struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp);

include/trace/events/page_pool.h

@@ -10,7 +10,7 @@
 
 #include <net/page_pool.h>
 
-TRACE_EVENT(page_pool_inflight,
+TRACE_EVENT(page_pool_release,
 
 	TP_PROTO(const struct page_pool *pool,
 		 s32 inflight, u32 hold, u32 release),
@@ -22,6 +22,7 @@ TRACE_EVENT(page_pool_inflight,
 		__field(s32,	inflight)
 		__field(u32,	hold)
 		__field(u32,	release)
+		__field(u64,	cnt)
 	),
 
 	TP_fast_assign(
@@ -29,10 +30,12 @@ TRACE_EVENT(page_pool_inflight,
 		__entry->inflight	= inflight;
 		__entry->hold		= hold;
 		__entry->release	= release;
+		__entry->cnt		= pool->destroy_cnt;
 	),
 
-	TP_printk("page_pool=%p inflight=%d hold=%u release=%u",
-	  __entry->pool, __entry->inflight, __entry->hold, __entry->release)
+	TP_printk("page_pool=%p inflight=%d hold=%u release=%u cnt=%llu",
+		__entry->pool, __entry->inflight, __entry->hold,
+		__entry->release, __entry->cnt)
 );
 
 TRACE_EVENT(page_pool_state_release,

net/core/page_pool.c

@@ -200,7 +200,7 @@ static s32 page_pool_inflight(struct page_pool *pool)
 
 	inflight = _distance(hold_cnt, release_cnt);
 
-	trace_page_pool_inflight(pool, inflight, hold_cnt, release_cnt);
+	trace_page_pool_release(pool, inflight, hold_cnt, release_cnt);
 	WARN(inflight < 0, "Negative(%d) inflight packet-pages", inflight);
 
 	return inflight;
@@ -349,10 +349,13 @@ static void page_pool_free(struct page_pool *pool)
 	kfree(pool);
 }
 
-static void page_pool_scrub(struct page_pool *pool)
+static void page_pool_empty_alloc_cache_once(struct page_pool *pool)
 {
 	struct page *page;
 
+	if (pool->destroy_cnt)
+		return;
+
 	/* Empty alloc cache, assume caller made sure this is
 	 * no-longer in use, and page_pool_alloc_pages() cannot be
 	 * call concurrently.
@@ -361,6 +364,12 @@ static void page_pool_scrub(struct page_pool *pool)
 		page = pool->alloc.cache[--pool->alloc.count];
 		__page_pool_return_page(pool, page);
 	}
+}
+
+static void page_pool_scrub(struct page_pool *pool)
+{
+	page_pool_empty_alloc_cache_once(pool);
+	pool->destroy_cnt++;
 
 	/* No more consumers should exist, but producers could still
 	 * be in-flight.