[PATCH bpf-next] net: Add a warning if NAPI cb missed xdp_do_flush().

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

A few drivers were missing a xdp_do_flush() invocation after
XDP_REDIRECT.

Add three helper functions each for one of the per-CPU lists. Return
true if the per-CPU list is non-empty and flush the list.
Add xdp_do_check_flushed() which invokes each helper functions and
creats a warning if one of the functions had a non-empty list.
Hide everything behind CONFIG_DEBUG_NET.

Suggested-by: Jesper Dangaard Brouer <hawk@kernel.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---

This is follow-up to
	https://lore.kernel.org/all/cb2f7931-5ae5-8583-acff-4a186fed6632@kernel.org

It has been compile tested.

 include/linux/bpf.h    | 16 ++++++++++++++++
 include/linux/filter.h |  8 ++++++++
 include/net/xdp_sock.h | 10 ++++++++++
 kernel/bpf/cpumap.c    | 10 ++++++++++
 kernel/bpf/devmap.c    | 10 ++++++++++
 net/core/dev.c         |  2 ++
 net/core/filter.c      | 14 ++++++++++++++
 net/xdp/xsk.c          | 10 ++++++++++
 8 files changed, 80 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 30063a760b5af..a4eb8f23d35e6 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2730,6 +2730,22 @@ static inline void bpf_dynptr_set_rdonly(struct bpf_dynptr_kern *ptr)
 }
 #endif /* CONFIG_BPF_SYSCALL */
 
+#if defined(CONFIG_BPF_SYSCALL) && defined(CONFIG_DEBUG_NET)
+bool __dev_check_flush(void);
+bool __cpu_map_check_flush(void);
+
+#else
+static inline bool __dev_check_flush(void)
+{
+	return false;
+}
+
+static inline bool __cpu_map_check_flush(void)
+{
+	return false;
+}
+#endif
+
 static __always_inline int
 bpf_probe_read_kernel_common(void *dst, u32 size, const void *unsafe_ptr)
 {
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 27406aee2d402..db095d731813e 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -1025,6 +1025,14 @@ int xdp_do_redirect_frame(struct net_device *dev,
 			  struct bpf_prog *prog);
 void xdp_do_flush(void);
 
+#ifdef CONFIG_DEBUG_NET
+void xdp_do_check_flushed(struct napi_struct *napi);
+
+#else
+static inline void xdp_do_check_flushed(struct napi_struct *napi) { }
+
+#endif
+
 /* The xdp_do_flush_map() helper has been renamed to drop the _map suffix, as
  * it is no longer only flushing maps. Keep this define for compatibility
  * until all drivers are updated - do not use xdp_do_flush_map() in new code!
diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h
index 69b472604b86f..c250b78712771 100644
--- a/include/net/xdp_sock.h
+++ b/include/net/xdp_sock.h
@@ -109,4 +109,14 @@ static inline void __xsk_map_flush(void)
 
 #endif /* CONFIG_XDP_SOCKETS */
 
+#if defined(CONFIG_XDP_SOCKETS) && defined(CONFIG_DEBUG_NET)
+bool __xsk_map_check_flush(void);
+
+#else
+static inline bool __xsk_map_check_flush(void)
+{
+	return false;
+}
+#endif
+
 #endif /* _LINUX_XDP_SOCK_H */
diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
index e42a1bdb7f536..2cded02d83815 100644
--- a/kernel/bpf/cpumap.c
+++ b/kernel/bpf/cpumap.c
@@ -764,6 +764,16 @@ void __cpu_map_flush(void)
 	}
 }
 
+#ifdef CONFIG_DEBUG_NET
+bool __cpu_map_check_flush(void)
+{
+	if (list_empty(this_cpu_ptr(&cpu_map_flush_list)))
+		return false;
+	__cpu_map_flush();
+	return true;
+}
+#endif
+
 static int __init cpu_map_init(void)
 {
 	int cpu;
diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index 4d42f6ed6c11a..8619ac1b879ed 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -418,6 +418,16 @@ void __dev_flush(void)
 	}
 }
 
+#ifdef CONFIG_DEBUG_NET
+bool __dev_check_flush(void)
+{
+	if (list_empty(this_cpu_ptr(&dev_flush_list)))
+		return false;
+	__dev_flush();
+	return true;
+}
+#endif
+
 /* Elements are kept alive by RCU; either by rcu_read_lock() (from syscall) or
  * by local_bh_disable() (from XDP calls inside NAPI). The
  * rcu_read_lock_bh_held() below makes lockdep accept both.
diff --git a/net/core/dev.c b/net/core/dev.c
index 606a366cc2095..9273b12ecf6fa 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6526,6 +6526,8 @@ static int __napi_poll(struct napi_struct *n, bool *repoll)
 	if (test_bit(NAPI_STATE_SCHED, &n->state)) {
 		work = n->poll(n, weight);
 		trace_napi_poll(n, work, weight);
+
+		xdp_do_check_flushed(n);
 	}
 
 	if (unlikely(work > weight))
diff --git a/net/core/filter.c b/net/core/filter.c
index a094694899c99..9841d0e32cb94 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -4207,6 +4207,20 @@ void xdp_do_flush(void)
 }
 EXPORT_SYMBOL_GPL(xdp_do_flush);
 
+#ifdef CONFIG_DEBUG_NET
+void xdp_do_check_flushed(struct napi_struct *napi)
+{
+	bool ret;
+
+	ret = __dev_check_flush();
+	ret |= __cpu_map_check_flush();
+	ret |= __xsk_map_check_flush();
+
+	WARN_ONCE(ret, "Missing xdp_do_flush() invocation after NAPI by %ps\n",
+		  napi->poll);
+}
+#endif
+
 void bpf_clear_redirect_map(struct bpf_map *map)
 {
 	struct bpf_redirect_info *ri;
diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 7482d0aca5046..4eae53478db07 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -391,6 +391,16 @@ void __xsk_map_flush(void)
 	}
 }
 
+#ifdef CONFIG_DEBUG_NET
+bool __xsk_map_check_flush(void)
+{
+	if (list_empty(this_cpu_ptr(&xskmap_flush_list)))
+		return false;
+	__xsk_map_flush();
+	return true;
+}
+#endif
+
 void xsk_tx_completed(struct xsk_buff_pool *pool, u32 nb_entries)
 {
 	xskq_prod_submit_n(pool->cq, nb_entries);
-- 
2.42.0