[PATCH 5.15 074/201] net: skb: introduce kfree_skb_reason()

Greg Kroah-Hartman
2022-07-27T17:12:50Z

From: Menglong Dong <imagedong@tencent.com>

[ Upstream commit c504e5c2f9648a1e5c2be01e8c3f59d394192bd3 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/skbuff.h | 23 ++++++++++++++++++++++-
include/trace/events/skb.h | 36 +++++++++++++++++++++++++++++-------
net/core/dev.c | 3 ++-
net/core/drop_monitor.c | 10 +++++++---
net/core/skbuff.c | 12 +++++++-----
5 files changed, 67 insertions(+), 17 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index e213acaa91ec..029bc228bcf9 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -304,6 +304,17 @@ 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.
@@ -1074,8 +1085,18 @@ 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 9e92f22eb086..294c61bbe44b 100644
--- 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 6111506a4105..12b1811cb488 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5005,7 +5005,8 @@ 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 1d99b731e5b2..78202141930f 100644
--- 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 @@ static void trace_drop_common(struct sk_buff *skb, void *location)
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);
}
@@ -494,7 +497,8 @@ 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 7ef0f5a8ab03..5ebef94e14dc 100644
--- 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)
{
--
2.35.1