Btrfs: ratelimit IO error printks

Btrfs has printks for various IO errors, including bad checksums and
mismatches between what we expect the block headers to contain and what
we actually find on the disk.

Longer term we need a real reporting mechanism for this, but for now
printk is going to have to do.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 2fdb299..552e08a 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1823,10 +1823,12 @@
 	return 0;
 
 zeroit:
-	printk(KERN_INFO "btrfs csum failed ino %lu off %llu csum %u "
-	       "private %llu\n", page->mapping->host->i_ino,
-	       (unsigned long long)start, csum,
-	       (unsigned long long)private);
+	if (printk_ratelimit()) {
+		printk(KERN_INFO "btrfs csum failed ino %lu off %llu csum %u "
+		       "private %llu\n", page->mapping->host->i_ino,
+		       (unsigned long long)start, csum,
+		       (unsigned long long)private);
+	}
 	memset(kaddr + offset, 1, end - start + 1);
 	flush_dcache_page(page);
 	kunmap_atomic(kaddr, KM_USER0);