Continuous SD IO causes hung task messages

[Russell King - ARM Linux admin]

Hi,

While dd'ing the contents of a SD card, I get hung task timeout
messages as per below.  However, the dd is making progress.  Any
ideas?

Presumably, mmc_rescan doesn't get a look-in while IO is progressing
for the card?

ARM64 host, Macchiatobin, uSD card.

Thanks.

root@arm-d06300000000:~# dd if=/dev/mmcblk1 | md5sum
INFO: task kworker/2:1:52 blocked for more than 120 seconds.
      Not tainted 5.2.0+ #309
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/2:1     D    0    52      2 0x00000028
Workqueue: events_freezable mmc_rescan
Call trace:
 __switch_to+0xb0/0x198
 __schedule+0x22c/0x604
 schedule+0x38/0xc8
 __mmc_claim_host+0xcc/0x1ec
 mmc_get_card+0x30/0x3c
 mmc_sd_detect+0x1c/0x78
 mmc_rescan+0x1c4/0x35c
 process_one_work+0x14c/0x408
 worker_thread+0x140/0x3f4
 kthread+0xfc/0x128
 ret_from_fork+0x10/0x18
INFO: task kworker/2:1:52 blocked for more than 120 seconds.
      Not tainted 5.2.0+ #309
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/2:1     D    0    52      2 0x00000028
Workqueue: events_freezable mmc_rescan
Call trace:
 __switch_to+0xb0/0x198
 __schedule+0x22c/0x604
 schedule+0x38/0xc8
 __mmc_claim_host+0xcc/0x1ec
 mmc_get_card+0x30/0x3c
 mmc_sd_detect+0x1c/0x78
 mmc_rescan+0x1c4/0x35c
 process_one_work+0x14c/0x408
 worker_thread+0x140/0x3f4
 kthread+0xfc/0x128
 ret_from_fork+0x10/0x18
INFO: task kworker/2:1:52 blocked for more than 241 seconds.
      Not tainted 5.2.0+ #309
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/2:1     D    0    52      2 0x00000028
Workqueue: events_freezable mmc_rescan
Call trace:
 __switch_to+0xb0/0x198
 __schedule+0x22c/0x604
 schedule+0x38/0xc8
 __mmc_claim_host+0xcc/0x1ec
 mmc_get_card+0x30/0x3c
 mmc_sd_detect+0x1c/0x78
 mmc_rescan+0x1c4/0x35c
 process_one_work+0x14c/0x408
 worker_thread+0x140/0x3f4
 kthread+0xfc/0x128
 ret_from_fork+0x10/0x18
INFO: task kworker/2:1:52 blocked for more than 362 seconds.
      Not tainted 5.2.0+ #309
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/2:1     D    0    52      2 0x00000028
Workqueue: events_freezable mmc_rescan
Call trace:
 __switch_to+0xb0/0x198
 __schedule+0x22c/0x604
 schedule+0x38/0xc8
 __mmc_claim_host+0xcc/0x1ec
 mmc_get_card+0x30/0x3c
 mmc_sd_detect+0x1c/0x78
 mmc_rescan+0x1c4/0x35c
 process_one_work+0x14c/0x408
 worker_thread+0x140/0x3f4
 kthread+0xfc/0x128
 ret_from_fork+0x10/0x18

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