page_pool: add tracepoints for page_pool with details need by XDP

The xdp tracepoints for mem id disconnect don't carry information about, why
it was not safe_to_remove. The tracepoint page_pool:page_pool_inflight in
this patch can be used for extract this info for further debugging.

This patchset also adds tracepoint for the pages_state_* release/hold
transitions, including a pointer to the page. This can be used for stats
about in-flight pages, or used to debug page leakage via keeping track of
page pointer and combining this with kprobe for __put_page().

Signed-off-by: Jesper Dangaard Brouer <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/trace/events/page_pool.h

···
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM page_pool
+
+#if !defined(_TRACE_PAGE_POOL_H) || defined(TRACE_HEADER_MULTI_READ)
+#define      _TRACE_PAGE_POOL_H
+
+#include <linux/types.h>
+#include <linux/tracepoint.h>
+
+#include <net/page_pool.h>
+
+TRACE_EVENT(page_pool_inflight,
+
+	TP_PROTO(const struct page_pool *pool,
+		 s32 inflight, u32 hold, u32 release),
+
+	TP_ARGS(pool, inflight, hold, release),
+
+	TP_STRUCT__entry(
+		__field(const struct page_pool *, pool)
+		__field(s32,	inflight)
+		__field(u32,	hold)
+		__field(u32,	release)
+	),
+
+	TP_fast_assign(
+		__entry->pool		= pool;
+		__entry->inflight	= inflight;
+		__entry->hold		= hold;
+		__entry->release	= release;
+	),
+
+	TP_printk("page_pool=%p inflight=%d hold=%u release=%u",
+	  __entry->pool, __entry->inflight, __entry->hold, __entry->release)
+);
+
+TRACE_EVENT(page_pool_state_release,
+
+	TP_PROTO(const struct page_pool *pool,
+		 const struct page *page, u32 release),
+
+	TP_ARGS(pool, page, release),
+
+	TP_STRUCT__entry(
+		__field(const struct page_pool *,	pool)
+		__field(const struct page *,		page)
+		__field(u32,				release)
+	),
+
+	TP_fast_assign(
+		__entry->pool		= pool;
+		__entry->page		= page;
+		__entry->release	= release;
+	),
+
+	TP_printk("page_pool=%p page=%p release=%u",
+		  __entry->pool, __entry->page, __entry->release)
+);
+
+TRACE_EVENT(page_pool_state_hold,
+
+	TP_PROTO(const struct page_pool *pool,
+		 const struct page *page, u32 hold),
+
+	TP_ARGS(pool, page, hold),
+
+	TP_STRUCT__entry(
+		__field(const struct page_pool *,	pool)
+		__field(const struct page *,		page)
+		__field(u32,				hold)
+	),
+
+	TP_fast_assign(
+		__entry->pool	= pool;
+		__entry->page	= page;
+		__entry->hold	= hold;
+	),
+
+	TP_printk("page_pool=%p page=%p hold=%u",
+		  __entry->pool, __entry->page, __entry->hold)
+);
+
+#endif /* _TRACE_PAGE_POOL_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>

net/core/net-traces.c

···
 EXPORT_TRACEPOINT_SYMBOL_GPL(br_fdb_update);
 #endif
 
+#if IS_ENABLED(CONFIG_PAGE_POOL)
+#include <trace/events/page_pool.h>
+#endif
+
 #include <trace/events/neigh.h>
 EXPORT_TRACEPOINT_SYMBOL_GPL(neigh_update);
 EXPORT_TRACEPOINT_SYMBOL_GPL(neigh_update_done);

net/core/page_pool.c

···
  *	Author:	Jesper Dangaard Brouer <[e-mail]>
  *	Copyright (C) 2016 Red Hat, Inc.
  */
+
 #include <linux/types.h>
 #include <linux/kernel.h>
 #include <linux/slab.h>
···
 #include <linux/dma-mapping.h>
 #include <linux/page-flags.h>
 #include <linux/mm.h> /* for __put_page() */
+
+#include <trace/events/page_pool.h>
 
 static int page_pool_init(struct page_pool *pool,
 			  const struct page_pool_params *params)
···
 	/* Track how many pages are held 'in-flight' */
 	pool->pages_state_hold_cnt++;
 
+	trace_page_pool_state_hold(pool, page, pool->pages_state_hold_cnt);
+
 	/* When page just alloc'ed is should/must have refcnt 1. */
 	return page;
 }
···
 
 	distance = _distance(hold_cnt, release_cnt);
 
-	/* TODO: Add tracepoint here */
+	trace_page_pool_inflight(pool, distance, hold_cnt, release_cnt);
 	return distance;
 }
 
···
 	page->dma_addr = 0;
 skip_dma_unmap:
 	atomic_inc(&pool->pages_state_release_cnt);
+	trace_page_pool_state_release(pool, page,
+			      atomic_read(&pool->pages_state_release_cnt));
 }
 
 /* unmap the page and clean our state */