ext4: add ratelimiting to ext4 messages

In the case of a storage device that suddenly disappears, or in the
case of significant file system corruption, this can result in a huge
flood of messages being sent to the console.  This can overflow the
file system containing /var/log/messages, or if a serial console is
configured, this can slow down the system so much that a hardware
watchdog can end up triggering forcing a system reboot.

Google-Bug-Id: 7258357

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index af815ea..65485ab 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -29,6 +29,7 @@
 #include <linux/wait.h>
 #include <linux/blockgroup_lock.h>
 #include <linux/percpu_counter.h>
+#include <linux/ratelimit.h>
 #include <crypto/hash.h>
 #ifdef __KERNEL__
 #include <linux/compat.h>
@@ -1314,6 +1315,11 @@
 	unsigned long s_es_last_sorted;
 	struct percpu_counter s_extent_cache_cnt;
 	spinlock_t s_es_lru_lock ____cacheline_aligned_in_smp;
+
+	/* Ratelimit ext4 messages. */
+	struct ratelimit_state s_err_ratelimit_state;
+	struct ratelimit_state s_warning_ratelimit_state;
+	struct ratelimit_state s_msg_ratelimit_state;
 };
 
 static inline struct ext4_sb_info *EXT4_SB(struct super_block *sb)