Would dd command block kworker?

allfox · Sat May 28, 2016 2:55 pm

I got a few "INFO" from kernel when doing sudo dd if=/dev/zero of=/dev/mmcblk0 bs=4M:

1305 May 28 21:19:22 pi1 kernel: [ 1200.164204] INFO: task kworker/u8:3:1233 blocked for more than 120 seconds.
1306 May 28 21:19:22 pi1 kernel: [ 1200.164226]       Not tainted 4.4.9-v7+ #884
1307 May 28 21:19:22 pi1 kernel: [ 1200.164234] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
1308 May 28 21:19:22 pi1 kernel: [ 1200.164246] kworker/u8:3    D 805b3864     0  1233      2 0x00000000
1309 May 28 21:19:22 pi1 kernel: [ 1200.164281] Workqueue: kmmcd mmc_rescan
1310 May 28 21:19:22 pi1 kernel: [ 1200.164312] [<805b3864>] (__schedule) from [<805b3ddc>] (schedule+0x50/0xa8)
1311 May 28 21:19:22 pi1 kernel: [ 1200.164332] [<805b3ddc>] (schedule) from [<8046a9d8>] (__mmc_claim_host+0xb8/0x1cc)
1312 May 28 21:19:22 pi1 kernel: [ 1200.164354] [<8046a9d8>] (__mmc_claim_host) from [<8046ab1c>] (mmc_get_card+0x30/0x34)
1313 May 28 21:19:22 pi1 kernel: [ 1200.164375] [<8046ab1c>] (mmc_get_card) from [<80472bdc>] (mmc_sd_detect+0x2c/0x80)
1314 May 28 21:19:22 pi1 kernel: [ 1200.164394] [<80472bdc>] (mmc_sd_detect) from [<8046d12c>] (mmc_rescan+0xc8/0x324)
1315 May 28 21:19:22 pi1 kernel: [ 1200.164417] [<8046d12c>] (mmc_rescan) from [<8003c634>] (process_one_work+0x154/0x458)
1316 May 28 21:19:22 pi1 kernel: [ 1200.164440] [<8003c634>] (process_one_work) from [<8003c98c>] (worker_thread+0x54/0x500)
1317 May 28 21:19:22 pi1 kernel: [ 1200.164460] [<8003c98c>] (worker_thread) from [<80042660>] (kthread+0xec/0x104)
1318 May 28 21:19:22 pi1 kernel: [ 1200.164480] [<80042660>] (kthread) from [<8000fbc8>] (ret_from_fork+0x14/0x2c)

The dd command itself finished normally.

Could anyone tell me if this is normal?

Background story:
I picked up a new SD card today. It is branded as Qilive 8GB class 10.
It should be genuine as I picked it from an Auchan market. Qilive is a brand from Auchan themselves: http://qilive.com/
Anyway, it's quite slow.
dd if=/dev/zero of=/dev/mmcblk0 bs=4M would speed at about 6MB/s. It advertised as class 10, so I think it should be at least 10MB/s.
dd if=/dev/mmcblk0 of=/dev/null bs=4M would speed at about 23MB/s. It advertised 30MB/s.
I'm using a Pi 3.