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SubjectBUG: drivers/pinctrl/core: races in pinctrl_groups and deferred probing
Date
Hi Linus,
we have sporadically observed this bug on OMAP3 and OMAP5 machines during boot:

> [ 5.988882] Unable to handle kernel NULL pointer dereference at virtual address 00000000
> [ 6.003089] pgd = (ptrval)
> [ 6.011859] [00000000] *pgd=ad268003, *pmd=27f089003
> [ 6.025112] ehci-omap 4a064c00.ehci: irq 146, io mem 0x4a064c00
> [ 6.032874] omapdss: unknown parameter 'def_disp' ignored
> [ 6.040373] bq24296_get_vsys_voltage(0)
> [ 6.052902] Internal error: Oops: 207 [#1] PREEMPT SMP ARM
> [ 6.058661] Modules linked in: encoder_tpd12s015(+) pwm_omap_dmtimer(+) connector_hdmi(+) omapdss(+) generic_adc_battery pwm_bl(+) omapdss_base cec ehci_omap(+) wlcore_sdio dwc3_omap leds_is31fl319x crtouch_mt tsc2007 bmp280_spi bq2429x_charger(+) bq27xxx_battery_i2c bq27xxx_battery ina2xx tca8418_keypad as5013(+) gpio_twl6040 twl6040_vibra palmas_pwrbutton palmas_gpadc bmc150_magn_i2c bmc150_accel_i2c usb3503 bmp280_i2c bmc150_accel_core bmc150_magn bmp280 industrialio_triggered_buffer w2cbw003_bluetooth bno055 kfifo_buf industrialio snd_soc_omap_mcpdm snd_soc_omap_mcbsp snd_soc_omap snd_pcm_dmaengine
> [ 6.114731] CPU: 0 PID: 1307 Comm: udevd Tainted: G W 4.17.0-letux-lpae+ #2406
> [ 6.123661] Hardware name: Generic OMAP5 (Flattened Device Tree)
> [ 6.129962] PC is at strcmp+0x0/0x34
> [ 6.133716] LR is at pinctrl_get_group_selector+0x44/0x78
> [ 6.139362] pc : [<c0849b98>] lr : [<c0526260>] psr: a00e0013
> [ 6.145920] sp : ed26dd00 ip : ed3ff390 fp : 00000019
> [ 6.151389] r10: 00000018 r9 : ed2dfb40 r8 : 00000019
> [ 6.156866] r7 : c088aba8 r6 : ebfcdb84 r5 : ee55f880 r4 : 00000017
> [ 6.163703] r3 : c05244a4 r2 : 00000000 r1 : ebfcdb84 r0 : 00000000
> [ 6.170548] Flags: NzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user
> [ 6.178026] Control: 30c5387d Table: ad245b80 DAC: fffffffd
> [ 6.184053] Process udevd (pid: 1307, stack limit = 0x(ptrval))
> [ 6.190258] Stack: (0xed26dd00 to 0xed26e000)
> [ 6.194823] dd00: ee55f880 ebfcdb84 00000000 ed0e7810 00000000 c0527220 ed2dfd90 00000001
> [ 6.203402] dd20: 00000002 ed2dfdc0 ed2dfb80 ed2dfbc0 ed0e7810 00000000 00000000 ed2dfb40
> [ 6.211977] dd40: 00000000 c0525a88 00000014 ee263680 c0e4bdf0 c09d4e04 ee22b810 00000000
> [ 6.220557] dd60: ed2dfe10 ee22b810 c0ec3aec fffffdfb bf20a014 0000002f 00000000 c0525c50
> [ 6.229135] dd80: 00000000 ee22b810 ed2dfe50 c05ead24 ee22b810 00000000 c0ec3af0 c05cbd88
> [ 6.237710] dda0: ee22b810 ee22b844 bf20a014 c0e57bf0 bf20a180 bf20a1b0 00000000 c05cc038
> [ 6.246275] ddc0: ee22b810 bf20a014 c05cbfb8 c05ca51c ee0dde58 ee1f5434 bf20a014 00000000
> [ 6.254856] dde0: ed15df80 c05cb3b4 bf2092de bf2092df 00000000 bf20a014 c0e8a360 bf20d000
> [ 6.263432] de00: 00000000 c05ccbdc c05cd400 bf20a080 c0e8a360 c0202c74 014000c0 c0840fd4
> [ 6.272006] de20: bf20a0c8 ed3ff688 ed3ff5c0 c09d32e4 ed313ec0 00000000 00000000 ed313e80
> [ 6.280582] de40: ed313e80 a00f0113 ed313140 ed313ec0 ee000000 014000c0 bf20a080 ed26df50
> [ 6.289157] de60: bf20a08c bf20a080 ed26df50 ed313140 00000000 c02a098c bf20a080 ed313140
> [ 6.297739] de80: bf20a080 ed26df50 bf20a08c c029f7d4 ffff8000 00007fff bf20a080 c029cb04
> [ 6.306309] dea0: 00000064 c085b2f4 f0b05460 b6dc49f8 00000000 00000003 ed1d8240 000024b0
> [ 6.314875] dec0: 00000000 c0347e60 00000003 00000000 00000000 00000000 00000000 00000000
> [ 6.323454] dee0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> [ 6.332028] df00: 00000000 00000000 7fffffff 00000000 b6dc49f8 00000006 0000017b c02011e4
> [ 6.340601] df20: ed26c000 00000000 000545c0 c029fb40 7fffffff 00000000 00000003 c03104bc
> [ 6.349179] df40: 00000002 f0b03000 000024b0 00000000 f0b03c20 f0b03000 000024b0 f0b04fb0
> [ 6.357754] df60: f0b04077 f0b04800 00003000 00003120 00000000 00000000 00000000 00001b08
> [ 6.366323] df80: 0000001e 0000001f 00000016 00000000 00000012 00000000 00000000 bed4e004
> [ 6.374899] dfa0: 00000000 c0201000 00000000 bed4e004 00000006 b6dc49f8 00000000 00000000
> [ 6.383480] dfc0: 00000000 bed4e004 00000000 0000017b 00020000 00037f78 00050048 000545c0
> [ 6.392056] dfe0: bed4dee0 bed4ded0 b6dbec4b b6ec9a42 800f0030 00000006 00000000 00000000
> [ 6.400640] [<c0849b98>] (strcmp) from [<c0526260>] (pinctrl_get_group_selector+0x44/0x78)
> [ 6.409317] [<c0526260>] (pinctrl_get_group_selector) from [<c0527220>] (pinmux_map_to_setting+0x158/0x1a0)
> [ 6.419533] [<c0527220>] (pinmux_map_to_setting) from [<c0525a88>] (create_pinctrl+0x1f0/0x2f8)
> [ 6.428664] [<c0525a88>] (create_pinctrl) from [<c0525c50>] (devm_pinctrl_get+0x2c/0x6c)
> [ 6.437146] [<c0525c50>] (devm_pinctrl_get) from [<c05ead24>] (pinctrl_bind_pins+0x3c/0x138)
> [ 6.446008] [<c05ead24>] (pinctrl_bind_pins) from [<c05cbd88>] (driver_probe_device+0xe8/0x318)
> [ 6.455131] [<c05cbd88>] (driver_probe_device) from [<c05cc038>] (__driver_attach+0x80/0xa4)
> [ 6.463983] [<c05cc038>] (__driver_attach) from [<c05ca51c>] (bus_for_each_dev+0x58/0x7c)
> [ 6.472556] [<c05ca51c>] (bus_for_each_dev) from [<c05cb3b4>] (bus_add_driver+0xcc/0x1e0)
> [ 6.481143] [<c05cb3b4>] (bus_add_driver) from [<c05ccbdc>] (driver_register+0x9c/0xe0)
> [ 6.489545] [<c05ccbdc>] (driver_register) from [<c0202c74>] (do_one_initcall+0xb4/0x248)
> [ 6.498136] [<c0202c74>] (do_one_initcall) from [<c02a098c>] (do_init_module+0x58/0x1d0)
> [ 6.506614] [<c02a098c>] (do_init_module) from [<c029f7d4>] (load_module+0xe04/0xfb0)
> [ 6.514821] [<c029f7d4>] (load_module) from [<c029fb40>] (sys_finit_module+0x88/0x90)
> [ 6.523041] [<c029fb40>] (sys_finit_module) from [<c0201000>] (ret_fast_syscall+0x0/0x4c)
> [ 6.531604] Exception stack(0xed26dfa8 to 0xed26dff0)
> [ 6.536899] dfa0: 00000000 bed4e004 00000006 b6dc49f8 00000000 00000000
> [ 6.545472] dfc0: 00000000 bed4e004 00000000 0000017b 00020000 00037f78 00050048 000545c0
> [ 6.554037] dfe0: bed4dee0 bed4ded0 b6dbec4b b6ec9a42
> [ 6.559339] Code: e3520000 e5e32001 1afffffb e12fff1e (e4d03001)
> [ 6.567709] ---[ end trace 1a9ebd5c1c7fe0e4 ]---

It is initially triggered by udev loading and probing a module.

Here is another bug trace:

> [ 13.671844] Unable to handle kernel NULL pointer dereference at virtual address 00000000
> [ 13.693389] pgd = (ptrval)
> [ 13.696380] [00000000] *pgd=00000000
> [ 13.700134] Internal error: Oops: 17 [#1] PREEMPT SMP ARM
> [ 13.705780] Modules linked in: snd_soc_gtm601 pwm_omap_dmtimer connector_analog_tv generic_adc_battery pwm_bl bq27xxx_battery_hdq bq27xxx_battery omap3_isp(+) videobuf2_dma_contig videobuf2_memops videobuf2_v4l2 videobuf2_common omap_hdq omap2430 snd_soc_omap_mcbsp(+) snd_soc_omap snd_pcm_dmaengine bmp280_i2c(+) bmp280 ov9655(+) v4l2_fwnode v4l2_common itg3200 at24 videodev phy_twl4030_usb tsc2007 hmc5843_i2c hmc5843_core bma180 musb_hdrc industrialio_triggered_buffer lis3lv02d_i2c media leds_tca6507 lis3lv02d kfifo_buf input_polldev gpio_twl4030 snd_soc_twl4030 twl4030_vibra twl4030_charger twl4030_pwrbutton twl4030_madc industrialio w2sg0004 gps_core w2cbw003_bluetooth ehci_omap omapdss omapdss_base cec
> [ 13.771331] CPU: 0 PID: 937 Comm: kworker/0:2 Not tainted 4.17.0-rc2-letux+ #2290
> [ 13.779174] Hardware name: Generic OMAP36xx (Flattened Device Tree)
> [ 13.785736] Workqueue: events deferred_probe_work_func
> [ 13.791107] PC is at strcmp+0x0/0x34
> [ 13.794860] LR is at pinctrl_get_group_selector+0x6c/0xa8
> [ 13.800506] pc : [<c0705afc>] lr : [<c0429840>] psr: 600f0013
> [ 13.807067] sp : dddf9e08 ip : 00000000 fp : 00000011
> [ 13.812530] r10: 0000000f r9 : 00000010 r8 : c0745b0c
> [ 13.817993] r7 : 00000000 r6 : ddc41600 r5 : df9c5274 r4 : 0000000e
> [ 13.824829] r3 : 600f0013 r2 : 00000002 r1 : df9c5274 r0 : 00000000
> [ 13.831665] Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none
> [ 13.839111] Control: 10c5387d Table: 9c88c019 DAC: 00000051
> [ 13.845123] Process kworker/0:2 (pid: 937, stack limit = 0x(ptrval))
> [ 13.851776] Stack: (0xdddf9e08 to 0xdddfa000)
> [ 13.856323] 9e00: dddf9e2c ddc41600 df9c5274 00000000 dcc99f10 00000000
> [ 13.864868] 9e20: dcc98b80 c042a808 dcc84110 00000001 00000002 dcc98e40 dcc5bd80 dcc85f40
> [ 13.873413] 9e40: dcc99f10 00000000 00000000 dcc98b80 00000000 c0429040 00000014 dda424c0
> [ 13.881988] 9e60: c0a58df0 c0876b8c dda47c10 00000000 dca09110 dda47c10 c0aca804 fffffdfb
> [ 13.890563] 9e80: bf282014 0000002c c0a94390 c0429208 00000000 dda47c10 dca09150 c04bb85c
> [ 13.899108] 9ea0: dda47c10 00000000 c0aca808 c049fb58 00000000 dddf9ee8 c049fe64 dda47c44
> [ 13.907714] 9ec0: df9bbe00 c0a02d00 00000000 c049e3b8 dd81be6c dcc3d738 dda47c10 c0a63258
> [ 13.916259] 9ee0: 00000001 c049f9d8 dda47c10 00000001 00000000 dda47c10 c0a63258 dda47c10
> [ 13.924804] 9f00: c0a9dba0 c049ef94 dda47c10 c0a63044 c0a63060 c049f4a4 c049f3b8 dde97900
> [ 13.933380] 9f20: c0a63078 df9b8c00 00000000 df9bbe00 c0a02d00 c0145dac dde97900 c0a63078
> [ 13.941955] 9f40: ffff9023 dde97900 df9b8c00 df9b8c00 dddf8000 df9b8c18 c0a02d00 dde97918
> [ 13.950500] 9f60: 00000008 c0146580 dda48240 dde09ec0 dde16640 00000000 dde97900 c01462c0
> [ 13.959075] 9f80: dd8b1ef0 dde09edc 00000000 c014a598 dde16640 c014a464 00000000 00000000
> [ 13.967620] 9fa0: 00000000 00000000 00000000 c01010e8 00000000 00000000 00000000 00000000
> [ 13.976196] 9fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> [ 13.984741] 9fe0: 00000000 00000000 00000000 00000000 00000013 00000000 00000000 00000000
> [ 13.993316] [<c0705afc>] (strcmp) from [<c0429840>] (pinctrl_get_group_selector+0x6c/0xa8)
> [ 14.001953] [<c0429840>] (pinctrl_get_group_selector) from [<c042a808>] (pinmux_map_to_setting+0x158/0x1a0)
> [ 14.012145] [<c042a808>] (pinmux_map_to_setting) from [<c0429040>] (create_pinctrl+0x1f0/0x2f8)
> [ 14.021240] [<c0429040>] (create_pinctrl) from [<c0429208>] (devm_pinctrl_get+0x2c/0x6c)
> [ 14.029724] [<c0429208>] (devm_pinctrl_get) from [<c04bb85c>] (pinctrl_bind_pins+0x3c/0x138)
> [ 14.038574] [<c04bb85c>] (pinctrl_bind_pins) from [<c049fb58>] (driver_probe_device+0xe8/0x318)
> [ 14.047668] [<c049fb58>] (driver_probe_device) from [<c049e3b8>] (bus_for_each_drv+0x84/0x94)
> [ 14.056610] [<c049e3b8>] (bus_for_each_drv) from [<c049f9d8>] (__device_attach+0x88/0xfc)
> [ 14.065155] [<c049f9d8>] (__device_attach) from [<c049ef94>] (bus_probe_device+0x28/0x80)
> [ 14.073730] [<c049ef94>] (bus_probe_device) from [<c049f4a4>] (deferred_probe_work_func+0xec/0x120)
> [ 14.083221] [<c049f4a4>] (deferred_probe_work_func) from [<c0145dac>] (process_one_work+0x244/0x464)
> [ 14.092803] [<c0145dac>] (process_one_work) from [<c0146580>] (worker_thread+0x2c0/0x3ec)
> [ 14.101348] [<c0146580>] (worker_thread) from [<c014a598>] (kthread+0x134/0x150)
> [ 14.109100] [<c014a598>] (kthread) from [<c01010e8>] (ret_from_fork+0x14/0x2c)
> [ 14.116638] Exception stack(0xdddf9fb0 to 0xdddf9ff8)
> [ 14.121917] 9fa0: 00000000 00000000 00000000 00000000
> [ 14.130462] 9fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> [ 14.139038] 9fe0: 00000000 00000000 00000000 00000000 00000013 00000000
> [ 14.145935] Code: e3520000 e5e32001 1afffffb e12fff1e (e4d03001)
> [ 14.299560] omap-mcbsp 49022000.mcbsp: ASoC: Failed to create component debugfs directory

This time it comes from the deferred_probe_work_func().

It does not happen always and depends on which drivers are auto-probed from device tree and
in which sequence (which depends a little on random hardware influences).

Now my theory, after inserting some printk and digging through the code, is:
* the pinctrl-group handling is not thread safe but udev module probing and deferred_probe_work_func
can run cuncurrently
* the radix tree (pin_group_tree) gets garbled (and is maybe not even the correct data structure)

Here are some details of my thoughts:

First of all, there is a warning that radix trees do not do any locking internally:

https://lwn.net/Articles/175432/

"One should note that none of the radix tree functions perform any sort of locking internally.
It is up to the caller to ensure that multiple threads do not corrupt the tree or get into
other sorts of unpleasant race conditions."

Now if I look into pinctrl_generic_add_group() and pinctrl_generic_get_group_name(),
pctldev->num_groups++ is not protected if pinctrl_generic_add_group() may be called by
two threads in parallel for the same pctldev. Hence a second thread may try to insert
a different node into the radix tree at the same selector index. This fails but there
is no error check - and the second entry is completely missing (but probably assumed to
be there).

Even worse in practise (examples above) seems to be that a driver failing to probe
(-EPROBE_DEFER) should do a call to pinctrl_generic_remove_group() in addition to an initial
pinctrl_generic_add_group(). This may happen multiple times in succession until the
driver finally probes successfully. Each time, num_groups is incremented/decremented.
So if two threads are working on driver probing the pctldev->num_groups may go back
and forward at unexpected times changing the insertion point of the other thread.

[Note: I could not verify that pinctrl_generic_remove_group() is ever called].

Another observation is that the code seems to assume that the selector numbers are
always in sequence and only the last one added is deleted by pinctrl_generic_remove_group().

But if I assume that a deferred driver waits quite a while before deciding to -EPROBE_DEFER,
other drivers may have been probed successfully by the other thread and have incremented
num_groups by more than 1 . Therefore the driver calling pinctrl_generic_remove_group() is
no longer the last one added.

In other words, the assumption seems to be that a radix-tree is an array where deleting
one entry in the middle reduces the index of the following ones and the reduced counter
gives the index of the first free index. But it is a sparse array and indexes are not
modified by insert/remove.

The result is that if several drivers are concurrently being probed (deferred_probe_work_func
executed concurrently to udevd probing), the assignment of the selector (aka radix tree
slot) defined by pctldev->num_groups may become wrong.

So entries may get lost and return NULL for gname in pinctrl_get_group_selector()
and as a result we see the strcmp(NULL). This is my theory about these kernel oopses.

Unfortunately I have no good idea how a solution could look like. One thing is
to add locking but there is a note in the comments of the pinctrl_generic functions
and there is mutex_lock(&pinctrl_maps_mutex); So there is something, but I am not
sure if all call paths are locked.

The other is to get the index/selection assignment right (which may even fail with
proper locking of the radix tree), maybe by using a different data structure than
a radix-tree.

Another observation after adding a printk to pinctrl_generic_add_group() is:

root@letux:~# dmesg|fgrep pinctrl_generic_add_group
[ 0.749481] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_hsusb2_pins selector=0
[ 0.751464] pinctrl_generic_add_group: pctldev=ee33a000 name=pinmux_hsusb2_2_pins selector=0
[ 0.752380] pinctrl_generic_add_group: pctldev=ee3f1e80 name=pinmux_mcbsp1_devconf0_pins selector=0
[ 0.753143] pinctrl_generic_add_group: pctldev=ee3f1d80 name=pinmux_tv_acbias_devconf1_pins selector=0
[ 0.770294] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_uart1_pins selector=1
[ 0.772094] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_uart2_pins selector=2
[ 0.773254] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_uart3_pins selector=3
[ 1.800659] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_twl4030_pins selector=4
[ 1.809997] pinctrl_generic_add_group: pctldev=ee33a080 name=pinmux_twl4030_vpins selector=0
[ 1.972412] pinctrl_generic_add_group: pctldev=ee33a000 name=spi_gpio_pinmux selector=1
[ 2.167144] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_mmc1_pins selector=5
[ 2.204040] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_wlan_irq_pin selector=6
[ 2.379150] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_gpmc_pins selector=7
[ 2.774627] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_wlan_pins selector=8
[ 2.791015] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_bt_pins selector=9
[ 2.806610] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_wlan_irq_pin selector=10
[ 5.240020] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_dss_dpi_pins selector=11
[ 5.874664] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_mcbsp1_pins selector=12
[ 5.988159] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_mcbsp2_pins selector=13
[ 5.997283] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_mcbsp3_pins selector=14
[ 6.089141] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_penirq_pins selector=14
[ 6.149841] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_mcbsp4_pins selector=15
[ 6.205993] pinctrl_generic_add_group: pctldev=ee33a200 name=hdq_pins selector=17
[ 6.390899] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_camera_pins selector=18
[ 6.580169] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_camera_pins selector=19

^^^ pin group added twice

[ 6.890899] pinctrl_generic_add_group: pctldev=ee33a200 name=backlight_pins_pinmux selector=20
[ 6.957489] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_camera_pins selector=20

^^^ same selector number allocated twice

[ 6.985687] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_camera_pins selector=21
[ 7.020538] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_camera_pins selector=22

^^^ 23 missing
[ 7.123748] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_camera_pins selector=24
[ 7.158721] pinctrl_generic_add_group: pctldev=ee33a200 name=backlight_pins_pinmux selector=25

^^^ another pin group added twice

[ 7.195953] pinctrl_generic_add_group: pctldev=ee33a200 name=modem_pins selector=26
[ 7.213104] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_camera_pins selector=26

^^^ same selector allocated twice, 27 is missing

[ 7.239318] pinctrl_generic_add_group: pctldev=ee33a200 name=backlight_pins_pinmux selector=28

^^^ repetition

[ 7.287414] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_camera_pins selector=29
[ 7.328491] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_camera_pins selector=30
[ 7.663543] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_camera_pins selector=31
[ 7.693725] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_camera_pins selector=32
[ 7.999755] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_camera_pins selector=33
[ 8.091491] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_pps_pins selector=34
[ 8.100219] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_camera_pins selector=34

^^^ another duplicate

[ 8.197174] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_camera_pins selector=36
[ 8.928436] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_camera_pins selector=37
[ 9.465606] pinctrl_generic_add_group: pctldev=ee33a200 name=pinmux_camera_pins selector=38
root@letux:~#

Which means that some groups are added multiple times and cleanup on EPROBE_DEFER doesn't work.

Well, this is my theory - which may be wrong. The only fact is the problem with strcmp(NULL, ...)
sporadically occuring.

So I hope that someone can make sense out of these findings and propose a patch to fix the real
bug (which may exist for quite a while and became more visible in 4.17-rc1 - but bisect attempts
failed due to the randomness).

BR and thanks,
Nikolaus



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