[BUG] drivers: staging: comedi: do not call blocking ops when !TASK_RUNNING; state=1

[Piotr Gregor]

Calling blocking operations from wrong context.
Kernel:

Linux piotrpc 4.4.70-rt83 #1 SMP PREEMPT RT Thu Jul 13 08:42:02 BST 2017 x86_64 GNU/Linux

[   80.542018] NOHZ: local_softirq_pending 80
[  125.175471] ------------[ cut here ]------------
[  125.175491] WARNING: CPU: 0 PID: 1497 at kernel/sched/core.c:7833 __might_sleep+0x9f/0xb0()
[  125.175728] do not call blocking ops when !TASK_RUNNING; state=1 set at [<ffffffffc0575741>] comedi_read+0x1a1/0x610 [comedi]
[  125.175735] Modules linked in: cpufreq_conservative cpufreq_powersave cpufreq_userspace cfg80211 nfsd auth_rpcgss oid_registry nfs_acl nfs lockd grace fscache sunrpc nls_ascii nls_cp437 vfat fat snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_codec_generic intel_rapl joydev intel_powerclamp coretemp kvm drbg efi_pstore ansi_cprng irqbypass crct10dif_pclmul crc32_pclmul ghash_clmulni_intel aesni_intel aes_x86_64 lrw gf128mul glue_helper ablk_helper cryptd i915 serio_raw pcspkr efivars snd_hda_intel amplc_dio200_pci(C) amplc_dio200_common(C) snd_hda_codec iTCO_wdt comedi_8254(C) comedi_pci(C) iTCO_vendor_support comedi(C) snd_hda_core snd_hwdep snd_pcm drm_kms_helper snd_timer drm snd mei_me soundcore mei i2c_algo_bit shpchp eeepc_wmi asus_wmi sparse_keymap mxm_wmi battery hci_uart btbcm btqca btintel
[  125.175824]  bluetooth
[  125.175825]  wmi
[  125.175826]  rfkill
[  125.175827]  video
[  125.175828]  intel_lpss_acpi
[  125.175830]  intel_lpss
[  125.175831]  evdev
[  125.175832]  mfd_core
[  125.175833]  acpi_als
[  125.175834]  acpi_pad
[  125.175835]  kfifo_buf
[  125.175836]  button
[  125.175838]  industrialio
[  125.175839]  fuse
[  125.175840]  parport_pc
[  125.175841]  ppdev
[  125.175842]  lp
[  125.175843]  parport
[  125.175844]  autofs4
[  125.175845]  ext4
[  125.175846]  crc16
[  125.175847]  mbcache
[  125.175848]  jbd2
[  125.175849]  hid_generic
[  125.175851]  usbhid
[  125.175852]  sg
[  125.175853]  sr_mod
[  125.175854]  cdrom
[  125.175855]  sd_mod
[  125.175856]  crc32c_intel
[  125.175857]  ahci
[  125.175858]  libahci
[  125.175859]  psmouse
[  125.175860]  xhci_pci
[  125.175861]  libata
[  125.175862]  r8169
[  125.175864]  i2c_i801
[  125.175865]  mii
[  125.175866]  xhci_hcd
[  125.175867]  tg3
[  125.175868]  ptp
[  125.175869]  scsi_mod
[  125.175870]  usbcore
[  125.175871]  pps_core
[  125.175872]  libphy
[  125.175873]  usb_common
[  125.175874]  fan
[  125.175875]  thermal
[  125.175876]  i2c_hid
[  125.175877]  hid
[  125.175878]  fjes

[  125.175926] CPU: 0 PID: 1497 Comm: txrx Tainted: G        WC      4.4.70-rt83 #1
[  125.175928] Hardware name: NOVATECH LTD PC-XB04472/H110M-C, BIOS 3019 01/06/2017
[  125.175935]  0000000000000000 ffff8802205b3cb0 ffffffff81387160 ffff8802205b3cf8
[  125.175940]  0000000000000009 ffff8802205b3ce8 ffffffff81089766 ffffffffc057ca60
[  125.175944]  00000000000002dc 0000000000000000 0000000000000001 0000000000000001
[  125.175945] Call Trace:
[  125.175955]  [<ffffffff81387160>] dump_stack+0x85/0xc5
[  125.175963]  [<ffffffff81089766>] warn_slowpath_common+0x86/0xe0
[  125.175971]  [<ffffffff8108980c>] warn_slowpath_fmt+0x4c/0x50
[  125.175980]  [<ffffffff81185577>] ? trace_preempt_on+0x1a7/0x2b0
[  125.175985]  [<ffffffff8168ca95>] ? schedule+0x55/0xe0
[  125.175994]  [<ffffffffc0575741>] ? comedi_read+0x1a1/0x610 [comedi]
[  125.176001]  [<ffffffffc0575741>] ? comedi_read+0x1a1/0x610 [comedi]
[  125.176005]  [<ffffffff810b6d0f>] __might_sleep+0x9f/0xb0
[  125.176012]  [<ffffffff811f54cb>] __might_fault+0x3b/0xb0
[  125.176020]  [<ffffffffc057597f>] comedi_read+0x3df/0x610 [comedi]
[  125.176034]  [<ffffffff810bebf0>] ? wake_up_process+0x20/0x20
[  125.176044]  [<ffffffff812406d8>] __vfs_read+0x28/0xe0
[  125.176053]  [<ffffffff812f1f06>] ? security_file_permission+0xa6/0xc0
[  125.176060]  [<ffffffff81240c53>] ? rw_verify_area+0x53/0xf0
[  125.176066]  [<ffffffff81240d79>] vfs_read+0x89/0x130
[  125.176074]  [<ffffffff81241b79>] SyS_read+0x49/0xb0
[  125.176084]  [<ffffffff81691876>] entry_SYSCALL_64_fastpath+0x16/0x7a
[  125.176095] ---[ end trace 0000000000000003 ]---


cheers,
Piotr