collected metric container_blkio_io_serviced_recursive_total: was collected before with the same name and label values

[sofat1989]

When we get the metrics of containerd, we get this kind of error

collected metric container_blkio_io_serviced_recursive_total label:<name:"container_id" value:"7d31271cc4fe549a789d0c6a2b3070e2eca1b5123776315a1d78e55ff40f5c84" > label:<name:"device" value:"/dev/sda" > label:<name:"major" value:"8" > label:<name:"minor" value:"0" > label:<name:"namespace" value:"k8s.io" > label:<name:"op" value:"Total" > gauge:<value:83 > was collected before with the same name and label values

After adding more logs, we find there are duplicated blkio entries returned by the func https://github.com/containerd/containerd/blob/master/vendor/github.com/containerd/cgroups/blkio.go#L75

[&BlkIOEntry{Op:Read,Device:/dev/sda,Major:8,Minor:0,Value:0,}
 &BlkIOEntry{Op:Write,Device:/dev/sda,Major:8,Minor:0,Value:1,}
 &BlkIOEntry{Op:Sync,Device:/dev/sda,Major:8,Minor:0,Value:0,} 
 &BlkIOEntry{Op:Async,Device:/dev/sda,Major:8,Minor:0,Value:1,}
 &BlkIOEntry{Op:Total,Device:/dev/sda,Major:8,Minor:0,Value:1,} 
   &BlkIOEntry{Op:Read,Device:/dev/sdb,Major:8,Minor:16,Value:35,}
    &BlkIOEntry{Op:Write,Device:/dev/sdb,Major:8,Minor:16,Value:0,} 
    &BlkIOEntry{Op:Sync,Device:/dev/sdb,Major:8,Minor:16,Value:35,} 
    &BlkIOEntry{Op:Async,Device:/dev/sdb,Major:8,Minor:16,Value:0,} 
    &BlkIOEntry{Op:Total,Device:/dev/sdb,Major:8,Minor:16,Value:35,} 
    &BlkIOEntry{Op:Read,Device:/dev/dm-0,Major:253,Minor:0,Value:35,}
     &BlkIOEntry{Op:Write,Device:/dev/dm-0,Major:253,Minor:0,Value:0,} 
     &BlkIOEntry{Op:Sync,Device:/dev/dm-0,Major:253,Minor:0,Value:35,} 
     &BlkIOEntry{Op:Async,Device:/dev/dm-0,Major:253,Minor:0,Value:0,} 
     &BlkIOEntry{Op:Total,Device:/dev/dm-0,Major:253,Minor:0,Value:35,}
     &BlkIOEntry{Op:Read,Device:/dev/sda,Major:8,Minor:0,Value:0,} 
     &BlkIOEntry{Op:Write,Device:/dev/sda,Major:8,Minor:0,Value:1,} 
    &BlkIOEntry{Op:Sync,Device:/dev/sda,Major:8,Minor:0,Value:0,} 
    &BlkIOEntry{Op:Async,Device:/dev/sda,Major:8,Minor:0,Value:1,} 
    &BlkIOEntry{Op:Total,Device:/dev/sda,Major:8,Minor:0,Value:1,} 
    &BlkIOEntry{Op:Read,Device:/dev/sdb,Major:8,Minor:16,Value:35,}
     &BlkIOEntry{Op:Write,Device:/dev/sdb,Major:8,Minor:16,Value:0,} 
     &BlkIOEntry{Op:Sync,Device:/dev/sdb,Major:8,Minor:16,Value:35,} 
     &BlkIOEntry{Op:Async,Device:/dev/sdb,Major:8,Minor:16,Value:0,} 
     &BlkIOEntry{Op:Total,Device:/dev/sdb,Major:8,Minor:16,Value:35,}]

The root cause:
we have both throttle.io_serviced and io_serviced_recursive, so the IoServicedRecursive will be added twice

{
			name:  "throttle.io_serviced",
			entry: &stats.Blkio.IoServicedRecursive,
		},

{
				name:  "io_serviced_recursive",
				entry: &stats.Blkio.IoServicedRecursive,
			},