net: skb: introduce kfree_skb_reason()

Introduce the interface kfree_skb_reason(), which is able to pass
the reason why the skb is dropped to 'kfree_skb' tracepoint.

Add the 'reason' field to 'trace_kfree_skb', therefor user can get
more detail information about abnormal skb with 'drop_monitor' or
eBPF.

All drop reasons are defined in the enum 'skb_drop_reason', and
they will be print as string in 'kfree_skb' tracepoint in format
of 'reason: XXX'.

( Maybe the reasons should be defined in a uapi header file, so that
user space can use them? )

Signed-off-by: Menglong Dong <imagedong@tencent.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 642acb0d1646b7635b12488160468ebde8c66637..ef0870abc791c959bf039eb432c3df06c205f1de 100644 (file)
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -305,6 +305,17 @@ struct sk_buff_head {
 
 struct sk_buff;
 
+/* The reason of skb drop, which is used in kfree_skb_reason().
+ * en...maybe they should be splited by group?
+ *
+ * Each item here should also be in 'TRACE_SKB_DROP_REASON', which is
+ * used to translate the reason to string.
+ */
+enum skb_drop_reason {
+       SKB_DROP_REASON_NOT_SPECIFIED,
+       SKB_DROP_REASON_MAX,
+};
+
 /* To allow 64K frame to be packed as single skb without frag_list we
  * require 64K/PAGE_SIZE pages plus 1 additional page to allow for
  * buffers which do not start on a page boundary.
@@ -1085,8 +1096,18 @@ static inline bool skb_unref(struct sk_buff *skb)
        return true;
 }
 
+void kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason);
+
+/**
+ *     kfree_skb - free an sk_buff with 'NOT_SPECIFIED' reason
+ *     @skb: buffer to free
+ */
+static inline void kfree_skb(struct sk_buff *skb)
+{
+       kfree_skb_reason(skb, SKB_DROP_REASON_NOT_SPECIFIED);
+}
+
 void skb_release_head_state(struct sk_buff *skb);
-void kfree_skb(struct sk_buff *skb);
 void kfree_skb_list(struct sk_buff *segs);
 void skb_dump(const char *level, const struct sk_buff *skb, bool full_pkt);
 void skb_tx_error(struct sk_buff *skb);

diff --git a/include/trace/events/skb.h b/include/trace/events/skb.h
index 9e92f22eb086c2b89b58d2fd9a37fe9ffc09edd2..294c61bbe44b6e65236e4c6e6297c26d9efab3b5 100644 (file)
--- a/include/trace/events/skb.h
+++ b/include/trace/events/skb.h
@@ -9,29 +9,51 @@
 #include <linux/netdevice.h>
 #include <linux/tracepoint.h>
 
+#define TRACE_SKB_DROP_REASON                                  \
+       EM(SKB_DROP_REASON_NOT_SPECIFIED, NOT_SPECIFIED)        \
+       EMe(SKB_DROP_REASON_MAX, MAX)
+
+#undef EM
+#undef EMe
+
+#define EM(a, b)       TRACE_DEFINE_ENUM(a);
+#define EMe(a, b)      TRACE_DEFINE_ENUM(a);
+
+TRACE_SKB_DROP_REASON
+
+#undef EM
+#undef EMe
+#define EM(a, b)       { a, #b },
+#define EMe(a, b)      { a, #b }
+
 /*
  * Tracepoint for free an sk_buff:
  */
 TRACE_EVENT(kfree_skb,
 
-       TP_PROTO(struct sk_buff *skb, void *location),
+       TP_PROTO(struct sk_buff *skb, void *location,
+                enum skb_drop_reason reason),
 
-       TP_ARGS(skb, location),
+       TP_ARGS(skb, location, reason),
 
        TP_STRUCT__entry(
-               __field(        void *,         skbaddr         )
-               __field(        void *,         location        )
-               __field(        unsigned short, protocol        )
+               __field(void *,         skbaddr)
+               __field(void *,         location)
+               __field(unsigned short, protocol)
+               __field(enum skb_drop_reason,   reason)
        ),
 
        TP_fast_assign(
                __entry->skbaddr = skb;
                __entry->location = location;
                __entry->protocol = ntohs(skb->protocol);
+               __entry->reason = reason;
        ),
 
-       TP_printk("skbaddr=%p protocol=%u location=%p",
-               __entry->skbaddr, __entry->protocol, __entry->location)
+       TP_printk("skbaddr=%p protocol=%u location=%p reason: %s",
+                 __entry->skbaddr, __entry->protocol, __entry->location,
+                 __print_symbolic(__entry->reason,
+                                  TRACE_SKB_DROP_REASON))
 );
 
 TRACE_EVENT(consume_skb,

diff --git a/net/core/dev.c b/net/core/dev.c
index 83a4089990a0af65364d4e244f60a83c7767cf8b..84a0d9542fe943fae6125e36352a123bec0e21e9 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4899,7 +4899,8 @@ static __latent_entropy void net_tx_action(struct softirq_action *h)
                        if (likely(get_kfree_skb_cb(skb)->reason == SKB_REASON_CONSUMED))
                                trace_consume_skb(skb);
                        else
-                               trace_kfree_skb(skb, net_tx_action);
+                               trace_kfree_skb(skb, net_tx_action,
+                                               SKB_DROP_REASON_NOT_SPECIFIED);
 
                        if (skb->fclone != SKB_FCLONE_UNAVAILABLE)
                                __kfree_skb(skb);

diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
index 3d0ab2eec91667bdfac93878a046fc727fc22b99..7b288a121a41a7b3f3e19e275d1da3ce50579b01 100644 (file)
--- a/net/core/drop_monitor.c
+++ b/net/core/drop_monitor.c
@@ -110,7 +110,8 @@ static u32 net_dm_queue_len = 1000;
 
 struct net_dm_alert_ops {
        void (*kfree_skb_probe)(void *ignore, struct sk_buff *skb,
-                               void *location);
+                               void *location,
+                               enum skb_drop_reason reason);
        void (*napi_poll_probe)(void *ignore, struct napi_struct *napi,
                                int work, int budget);
        void (*work_item_func)(struct work_struct *work);
@@ -262,7 +263,9 @@ out:
        spin_unlock_irqrestore(&data->lock, flags);
 }
 
-static void trace_kfree_skb_hit(void *ignore, struct sk_buff *skb, void *location)
+static void trace_kfree_skb_hit(void *ignore, struct sk_buff *skb,
+                               void *location,
+                               enum skb_drop_reason reason)
 {
        trace_drop_common(skb, location);
 }
@@ -490,7 +493,8 @@ static const struct net_dm_alert_ops net_dm_alert_summary_ops = {
 
 static void net_dm_packet_trace_kfree_skb_hit(void *ignore,
                                              struct sk_buff *skb,
-                                             void *location)
+                                             void *location,
+                                             enum skb_drop_reason reason)
 {
        ktime_t tstamp = ktime_get_real();
        struct per_cpu_dm_data *data;

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index e514a36bcffcc872d93db6a2abd2b4d14bd41e1d..0118f0afaa4fce8da167ddf39de4c9f3880ca05b 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -759,21 +759,23 @@ void __kfree_skb(struct sk_buff *skb)
 EXPORT_SYMBOL(__kfree_skb);
 
 /**
- *     kfree_skb - free an sk_buff
+ *     kfree_skb_reason - free an sk_buff with special reason
  *     @skb: buffer to free
+ *     @reason: reason why this skb is dropped
  *
  *     Drop a reference to the buffer and free it if the usage count has
- *     hit zero.
+ *     hit zero. Meanwhile, pass the drop reason to 'kfree_skb'
+ *     tracepoint.
  */
-void kfree_skb(struct sk_buff *skb)
+void kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason)
 {
        if (!skb_unref(skb))
                return;
 
-       trace_kfree_skb(skb, __builtin_return_address(0));
+       trace_kfree_skb(skb, __builtin_return_address(0), reason);
        __kfree_skb(skb);
 }
-EXPORT_SYMBOL(kfree_skb);
+EXPORT_SYMBOL(kfree_skb_reason);
 
 void kfree_skb_list(struct sk_buff *segs)
 {