Cannot attach some processes by ptrace?

Question

OS: Android 4.3 & 4.4 (root)

Hi all, I try to attach all the processes by calling ptrace(), my tested app can be attached but some processes can't be, for which I list them below:

I guess the reason may be its special properties, but what's the detail and root cause? Thank you!

a2mp ad_calc_wq aicl_check_wq apr_driver bam_dmux_rx batt_timer bdi-default binder button cable_detect cfg80211 cfinteractive charger_ctrl_ti crypto dbs_sync/0 deferwq detect devfreq_wq diag_cntl_wq ecryptfs-kthrea ext4-dio-unwrit f_mtp f9923000.spi file-storage flush-179:0 fsnotify_mark hdmi_tx_workq ipc_rtr_q6_ipcr IPCRTR irq/102-msm_iom jbd2/mmcblk0p22 k_gserial kblockd kdbs_up/0 keychord kgsl_devfreq_wq khelper khubd kpsmoused krfcommd ksoftirqd/0 kswapd0 kthreadd kworker/0:0 l2cap MC_Thread mcu_poll_reuqes mdss_dsi_event mhl_sii8240_855 migration/0 mmc_stats mmcqd/0 modem_notifier monitor_tsense_ mpm netns ngd_msm_ctrl_ng nmea ONEWIRE_WQ perflock_setrat pm_workerq_venu qmi qpnp-gpled rpm-smd rq_stats rt5506_gpio_off RX_Thread sb-1 sii8240_sii8558 smd_channel_clo smsm_cb_wq suspend_sys_syn SYN_ATT_reuqest sync_supers system tps61310_wq TX_Thread uether usb_bam_wq watchdog/0 ...

Answer 1

Those are kernel threads, not user-space processes.