Hi Johannes, et al.,
Sorry to bring the bearer of bad news, but your commit 2a5a8fa8b23
("leds: trigger: use RCU to protect the led_cdevs list"),
is causing the following RCU warning when used with blinking
triggers on I2C LED controllers which support hw blinking.
The specific problem is drivers/leds/led-triggers.c:
led_trigger_blink_setup() which does:
rcu_read_lock();
list_for_each_entry_rcu(led_cdev, &trig->led_cdevs, trig_list) {
if (oneshot)
led_blink_set_oneshot(led_cdev, delay_on, delay_off,
invert);
else
led_blink_set(led_cdev, delay_on, delay_off);
}
rcu_read_unlock();
And that led_blink_set() call then hits this path:
if (!test_bit(LED_BLINK_ONESHOT, &led_cdev->work_flags) &&
led_cdev->blink_set &&
!led_cdev->blink_set(led_cdev, delay_on, delay_off))
return;
Which calls directly into the LED controller driver which
talks to the LED controller over I2C which may sleep.
AFAICT (not much RCU experience) the problem basically is that in
a rcu_read_lock() section the code may not sleep. While
led_blink_set() can sleep. For completeness sake I've added
the full backtrace at the end of this email, but it really is not
that interesting.
>From the original commit I understand that RCU was chosen
because of other hairy issues. For non blinking triggers this
works fine, because led_set_brightness() is guaranteed to
not sleep using a workqueue to delay the set brightness
in case it would sleep.
We could do something similar for led_set_blink, at least
when called from led_trigger_blink[_oneshot], to avoid
this issue.
But I wonder if someone has any better ideas ?
Regards,
Hans
[ 832.605062] ------------[ cut here ]------------
[ 832.605085] Voluntary context switch within RCU read-side critical section!
[ 832.605119] WARNING: CPU: 2 PID: 370 at kernel/rcu/tree_plugin.h:318 rcu_note_context_switch+0x4ee/0x690
[ 832.605175] Modules linked in: snd_seq_dummy snd_hrtimer joydev wacom bq25890_charger(E) bq27xxx_battery_i2c(E) i2c_hid_of(E) goodix_ts hideep lp855x_bl bq27xxx_battery(E) snd_soc_sst_byt_cht_nocodec qrtr brcmfmac_wcc mei_pxp dwc3 mei_hdcp intel_powerclamp coretemp kvm_intel intel_rapl_msr gpio_keys x86_android_tablets(E) udc_core ulpi brcmfmac kvm brcmutil irqbypass i2c_cht_wc intel_cstate snd_sof_acpi_intel_byt cfg80211 snd_sof_acpi snd_sof_intel_atom leds_cht_wcove(E) snd_sof_xtensa_dsp snd_sof pcspkr extcon_intel_cht_wc snd_sof_utils lpc_ich snd_intel_sst_acpi intel_xhci_usb_role_switch snd_soc_acpi_intel_match snd_intel_sst_core snd_soc_sst_atom_hifi2_platform hid_sensor_magn_3d snd_soc_acpi snd_intel_dspcfg snd_intel_sdw_acpi hid_sensor_gyro_3d hid_sensor_accel_3d hid_sensor_incl_3d hid_sensor_rotation hid_sensor_als hid_sensor_trigger hid_sensor_iio_common industrialio_triggered_buffer kfifo_buf industrialio snd_soc_core snd_compress ac97_bus hci_uart(E) btqca(E) btrtl(E) btbcm(E) snd_pcm_dmaengine btintel(E)
[ 832.605676] snd_hdmi_lpe_audio intel_hid sparse_keymap intel_soc_pmic_bxtwc snd_seq bluetooth snd_seq_device ov5693 snd_pcm atomisp_ov2722(C) v4l2_fwnode v4l2_async atomisp_gmin_platform(C) videodev spi_pxa2xx_platform mc ecdh_generic snd_timer rfkill_gpio processor_thermal_device_pci_legacy snd rfkill dw_dmac processor_thermal_device soundcore processor_thermal_rfim processor_thermal_mbox mei_txe processor_thermal_rapl vfat fat int3400_thermal intel_rapl_common int3403_thermal mei soc_button_array int3406_thermal acpi_thermal_rel int340x_thermal_zone dptf_power(E) intel_soc_dts_iosf intel_int0002_vgpio dwc3_pci acpi_pad(E) zram hid_sensor_hub intel_ishtp_hid i915(E) crct10dif_pclmul mmc_block crc32_pclmul crc32c_intel i2c_algo_bit drm_buddy(E) drm_display_helper(E) ghash_clmulni_intel sha512_ssse3 wdat_wdt intel_ish_ipc cec video(E) intel_ishtp sdhci_acpi ttm(E) sdhci wmi i2c_hid_acpi(E) i2c_hid(E) mmc_core pwm_lpss_platform pwm_lpss ip6_tables ip_tables i2c_dev fuse
[ 832.606213] CPU: 2 PID: 370 Comm: kworker/2:4 Tainted: G WC E 6.3.0-rc4+ #179
[ 832.606237] Hardware name: Intel Corporation CHERRYVIEW D1 PLATFORM/Cherry Trail Tablet, BIOS CHTTYETI.X64.0514.R1B.1701240934 01/24/2017
[ 832.606251] Workqueue: events power_supply_changed_work
[ 832.606281] RIP: 0010:rcu_note_context_switch+0x4ee/0x690
[ 832.606311] Code: 49 89 3f 49 83 bc 24 98 00 00 00 00 0f 85 66 fe ff ff e9 58 fe ff ff 48 c7 c7 48 e4 75 83 c6 05 b9 0c b2 01 01 e8 92 4b f5 ff <0f> 0b e9 70 fb ff ff a9 ff ff ff 7f 0f 84 2c fc ff ff 65 48 8b 3c
[ 832.606328] RSP: 0018:ffffbd0480737908 EFLAGS: 00010092
[ 832.606348] RAX: 000000000000003f RBX: ffff9ff8fa933900 RCX: 0000000000000000
[ 832.606362] RDX: 0000000000000003 RSI: ffffffff837b6da0 RDI: 00000000ffffffff
[ 832.606374] RBP: 0000000000000000 R08: 0000000000000000 R09: ffffbd04807377c0
[ 832.606386] R10: 0000000000000003 R11: ffffffff83b44168 R12: ffff9ff8fa932a80
[ 832.606398] R13: ffff9ff8867a0000 R14: ffffbd0480737a78 R15: ffff9ff8810e5060
[ 832.606411] FS: 0000000000000000(0000) GS:ffff9ff8fa900000(0000) knlGS:0000000000000000
[ 832.606427] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 832.606439] CR2: 00007f1e96b510c8 CR3: 0000000155a20000 CR4: 00000000001006e0
[ 832.606453] Call Trace:
[ 832.606466] <TASK>
[ 832.606487] __schedule+0x9f/0x1480
[ 832.606527] schedule+0x5d/0xe0
[ 832.606549] schedule_timeout+0x79/0x140
[ 832.606572] ? __pfx_process_timeout+0x10/0x10
[ 832.606599] wait_for_completion_timeout+0x6f/0x140
[ 832.606627] i2c_dw_xfer+0x101/0x460
[ 832.606659] ? psi_group_change+0x168/0x400
[ 832.606680] __i2c_transfer+0x172/0x6d0
[ 832.606709] i2c_smbus_xfer_emulated+0x27d/0x9c0
[ 832.606732] ? __schedule+0x430/0x1480
[ 832.606753] ? preempt_count_add+0x6a/0xa0
[ 832.606778] ? get_nohz_timer_target+0x18/0x190
[ 832.606796] ? lock_timer_base+0x61/0x80
[ 832.606817] ? preempt_count_add+0x6a/0xa0
[ 832.606842] __i2c_smbus_xfer+0xa2/0x3f0
[ 832.606862] i2c_smbus_xfer+0x66/0xf0
[ 832.606882] i2c_smbus_read_byte_data+0x41/0x70
[ 832.606901] ? _raw_spin_unlock_irqrestore+0x23/0x40
[ 832.606922] ? __pm_runtime_suspend+0x46/0xc0
[ 832.606946] cht_wc_byte_reg_read+0x2e/0x60
[ 832.606972] _regmap_read+0x5c/0x120
[ 832.606997] _regmap_update_bits+0x96/0xc0
[ 832.607023] regmap_update_bits_base+0x5b/0x90
[ 832.607053] cht_wc_leds_brightness_get+0x412/0x910 [leds_cht_wcove]
[ 832.607094] led_blink_setup+0x28/0x100
[ 832.607119] led_trigger_blink+0x40/0x70
[ 832.607145] power_supply_update_leds+0x1b7/0x1c0
[ 832.607174] power_supply_changed_work+0x67/0xe0
[ 832.607198] process_one_work+0x1c8/0x3c0
[ 832.607222] worker_thread+0x4d/0x380
[ 832.607243] ? __pfx_worker_thread+0x10/0x10
[ 832.607258] kthread+0xe9/0x110
[ 832.607279] ? __pfx_kthread+0x10/0x10
[ 832.607300] ret_from_fork+0x2c/0x50
[ 832.607337] </TASK>
[ 832.607344] ---[ end trace 0000000000000000 ]---
