[PATCH net-next RFC 1/6] netconsole: add a per-target message rate limit

[Breno Leitao <leitao@debian.org>]

Give each target a token bucket and consult it once per message in
netconsole_write().

The bucket is created with a zero interval, which struct ratelimit_state
treats as unlimited, and nothing can set a nonzero one yet, so no target
changes behaviour.

Skip the bucket while oops_in_progress is set, so a limit configured for
steady-state logging never truncates an oops, BUG() or panic().

The configfs files that expose it come next.

___ratelimit() only trylocks its own raw spinlock, so it is safe with
target_list_lock held and interrupts disabled, and safe from NMI.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 drivers/net/netconsole.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index b358e5c367351..2ad514afa2b89 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -49,6 +49,7 @@
 #include <linux/rtnetlink.h>
 #include <linux/workqueue.h>
 #include <linux/delay.h>
+#include <linux/ratelimit.h>
 
 MODULE_AUTHOR("Matt Mackall <mpm@selenic.com>");
 MODULE_DESCRIPTION("Console driver for network interfaces");
@@ -175,6 +176,7 @@ struct netcons_userdata {
  * @sysdata:		Cached, formatted string of append
  * @sysdata_fields:	Sysdata features enabled.
  * @msgcounter:	Message sent counter.
+ * @ratelimit:	Opaque structure to ratelimit messages
  * @stats:	Packet send stats for the target. Used for debugging.
  * @state:	State of the target.
  *		Visible from userspace (read-write).
@@ -219,6 +221,7 @@ struct netconsole_target {
 	u32			sysdata_fields;
 	/* protected by target_list_lock */
 	u32			msgcounter;
+	struct ratelimit_state	ratelimit;
 #endif
 	struct netconsole_target_stats stats;
 	enum target_state	state;
@@ -282,6 +285,21 @@ static void dynamic_netconsole_mutex_unlock(void)
 	mutex_unlock(&dynamic_netconsole_mutex);
 }
 
+static void netconsole_ratelimit_init(struct netconsole_target *nt)
+{
+	ratelimit_state_init(&nt->ratelimit, 0, DEFAULT_RATELIMIT_BURST);
+	ratelimit_set_flags(&nt->ratelimit, RATELIMIT_MSG_ON_RELEASE);
+}
+
+static bool netconsole_ratelimited(struct netconsole_target *nt)
+{
+	/* A limit meant for steady-state logging must not eat a crash dump. */
+	if (oops_in_progress)
+		return false;
+
+	return !__ratelimit(&nt->ratelimit);
+}
+
 #else	/* !CONFIG_NETCONSOLE_DYNAMIC */
 
 static int __init dynamic_netconsole_init(void)
@@ -318,6 +336,15 @@ static void dynamic_netconsole_mutex_unlock(void)
 {
 }
 
+static void netconsole_ratelimit_init(struct netconsole_target *nt)
+{
+}
+
+static bool netconsole_ratelimited(struct netconsole_target *nt)
+{
+	return false;
+}
+
 #endif	/* CONFIG_NETCONSOLE_DYNAMIC */
 
 /* Check if the target was bound by mac address. */
@@ -686,6 +713,7 @@ static struct netconsole_target *alloc_and_init(void)
 	nt->remote_port = 6666;
 	eth_broadcast_addr(nt->remote_mac);
 	nt->state = STATE_DISABLED;
+	netconsole_ratelimit_init(nt);
 	INIT_WORK(&nt->resume_wq, process_resume_target);
 	/* Set up the skb pool primitives once; enabling only refills it. */
 	skb_queue_head_init(&nt->skb_pool);
@@ -2482,6 +2510,9 @@ static void netconsole_write(struct nbcon_write_context *wctxt, bool extended)
 		    !netif_running(nt->np.dev))
 			continue;
 
+		if (netconsole_ratelimited(nt))
+			continue;
+
 		/* If nbcon_enter_unsafe() fails, just return given netconsole
 		 * lost the ownership, and iterating over the targets will not
 		 * be able to re-acquire.

-- 
2.53.0-Meta