From 78158d134b056ceb974292e40a58e5f8a9af4cbe Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>
Date: Thu, 19 Sep 2019 18:01:23 +0200
Subject: [PATCH] basic/log: put a ratelimit on our logging to /dev/kmsg

See the inline comment for details.
---
 src/basic/log.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/src/basic/log.c b/src/basic/log.c
index 8bcc18bc80..f26b592a6c 100644
--- a/src/basic/log.c
+++ b/src/basic/log.c
@@ -29,6 +29,7 @@
 #include "parse-util.h"
 #include "proc-cmdline.h"
 #include "process-util.h"
+#include "ratelimit.h"
 #include "signal-util.h"
 #include "socket-util.h"
 #include "stdio-util.h"
@@ -459,6 +460,15 @@ static int write_to_kmsg(
                 const char *func,
                 const char *buffer) {
 
+        /* Set a ratelimit on the amount of messages logged to /dev/kmsg. This is mostly supposed to be a
+         * safety catch for the case where start indiscriminately logging in a loop. It will not catch cases
+         * where we log excessively, but not in a tight loop.
+         *
+         * Note that this ratelimit is per-emitter, so we might still overwhelm /dev/kmsg with multiple
+         * loggers.
+         */
+        static thread_local RateLimit ratelimit = { 5 * USEC_PER_SEC, 200 };
+
         char header_priority[2 + DECIMAL_STR_MAX(int) + 1],
              header_pid[4 + DECIMAL_STR_MAX(pid_t) + 1];
         struct iovec iovec[5] = {};
@@ -466,6 +476,9 @@ static int write_to_kmsg(
         if (kmsg_fd < 0)
                 return 0;
 
+        if (!ratelimit_below(&ratelimit))
+                return 0;
+
         xsprintf(header_priority, "<%i>", level);
         xsprintf(header_pid, "["PID_FMT"]: ", getpid_cached());