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SubjectRe: [Kernel] BUG: spinlock vs. mutex in SyS_finit_module / usbhs_runtime_resume / omap_tll_enable / clk_prepare_lock
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Hi Roger,

> Am 02.05.2016 um 15:03 schrieb H. Nikolaus Schaller <hns@goldelico.com>:
>
> Hi Roger,
>
>> Am 02.05.2016 um 14:41 schrieb Roger Quadros <rogerq@ti.com>:
>>
>> Hi Nikolaus,
>>
>> On 30/04/16 20:24, H. Nikolaus Schaller wrote:
>>> Hi,
>>> I have observed this kernel oops on an omap5 board from time to time (approx. 1% of boot processes):
>>>
>>> [ 5.830970] ehci-omap: OMAP-EHCI Host Controller driver
>>> [ 5.830974] driver_register 'ehci-omap'
>>> [ 5.895849] driver_register 'wl1271_sdio'
>>> [ 5.896870] BUG: scheduling while atomic: udevd/994/0x00000002
>>> [ 5.896876] 4 locks held by udevd/994:
>>> [ 5.896904] #0: (&dev->mutex){......}, at: [<c049597c>] __driver_attach+0x60/0xac
>>> [ 5.896923] #1: (&dev->mutex){......}, at: [<c049598c>] __driver_attach+0x70/0xac
>>> [ 5.896946] #2: (tll_lock){+.+...}, at: [<c04c2630>] omap_tll_enable+0x2c/0xd0
>>> [ 5.896966] #3: (prepare_lock){+.+...}, at: [<c05ce9c8>] clk_prepare_lock+0x48/0xe0
>>> [ 5.897042] Modules linked in: wlcore_sdio(+) ehci_omap(+) dwc3_omap snd_soc_ts3a225e leds_is31fl319x bq27xxx_battery_i2c tsc2007 bq27xxx_battery bq2429x_charger ina2xx tca8418_keypad as5013 leds_tca6507 twl6040_vibra gpio_twl6040 bmp085_i2c(+) palmas_gpadc usb3503 palmas_pwrbutton bmg160_i2c(+) bmp085 bma150(+) bmg160_core bmp280 input_polldev snd_soc_omap_mcbsp snd_soc_omap_mcpdm snd_soc_omap snd_pcm_dmaengine
>>> [ 5.897048] Preemption disabled at:[< (null)>] (null)
>>> [ 5.897051]
>>> [ 5.897059] CPU: 0 PID: 994 Comm: udevd Not tainted 4.6.0-rc5-letux+ #233
>>> [ 5.897062] Hardware name: Generic OMAP5 (Flattened Device Tree)
>>> [ 5.897076] [<c010e714>] (unwind_backtrace) from [<c010af34>] (show_stack+0x10/0x14)
>>> [ 5.897087] [<c010af34>] (show_stack) from [<c040aa7c>] (dump_stack+0x88/0xc0)
>>> [ 5.897099] [<c040aa7c>] (dump_stack) from [<c020c558>] (__schedule_bug+0xac/0xd0)
>>> [ 5.897111] [<c020c558>] (__schedule_bug) from [<c06f3d44>] (__schedule+0x88/0x7e4)
>>> [ 5.897120] [<c06f3d44>] (__schedule) from [<c06f46d8>] (schedule+0x9c/0xc0)
>>> [ 5.897129] [<c06f46d8>] (schedule) from [<c06f4904>] (schedule_preempt_disabled+0x14/0x20)
>>> [ 5.897140] [<c06f4904>] (schedule_preempt_disabled) from [<c06f64e4>] (mutex_lock_nested+0x258/0x43c)
>>> [ 5.897150] [<c06f64e4>] (mutex_lock_nested) from [<c05ce9c8>] (clk_prepare_lock+0x48/0xe0)
>>> [ 5.897160] [<c05ce9c8>] (clk_prepare_lock) from [<c05d0e7c>] (clk_prepare+0x10/0x28)
>>> [ 5.897169] [<c05d0e7c>] (clk_prepare) from [<c04c2668>] (omap_tll_enable+0x64/0xd0)
>>> [ 5.897180] [<c04c2668>] (omap_tll_enable) from [<c04c1728>] (usbhs_runtime_resume+0x18/0x17c)
>>> [ 5.897192] [<c04c1728>] (usbhs_runtime_resume) from [<c049d404>] (pm_generic_runtime_resume+0x2c/0x40)
>>> [ 5.897202] [<c049d404>] (pm_generic_runtime_resume) from [<c049f180>] (__rpm_callback+0x38/0x68)
>>> [ 5.897210] [<c049f180>] (__rpm_callback) from [<c049f220>] (rpm_callback+0x70/0x88)
>>> [ 5.897218] [<c049f220>] (rpm_callback) from [<c04a0a00>] (rpm_resume+0x4ec/0x7ec)
>>> [ 5.897227] [<c04a0a00>] (rpm_resume) from [<c04a0f48>] (__pm_runtime_resume+0x4c/0x64)
>>> [ 5.897236] [<c04a0f48>] (__pm_runtime_resume) from [<c04958dc>] (driver_probe_device+0x30/0x70)
>>> [ 5.897246] [<c04958dc>] (driver_probe_device) from [<c04959a4>] (__driver_attach+0x88/0xac)
>>> [ 5.897256] [<c04959a4>] (__driver_attach) from [<c04940f8>] (bus_for_each_dev+0x50/0x84)
>>> [ 5.897267] [<c04940f8>] (bus_for_each_dev) from [<c0494e40>] (bus_add_driver+0xcc/0x1e4)
>>> [ 5.897276] [<c0494e40>] (bus_add_driver) from [<c0496914>] (driver_register+0xac/0xf4)
>>> [ 5.897286] [<c0496914>] (driver_register) from [<c01018e0>] (do_one_initcall+0x100/0x1b8)
>>> [ 5.897296] [<c01018e0>] (do_one_initcall) from [<c01c7a54>] (do_init_module+0x58/0x1c0)
>>> [ 5.897304] [<c01c7a54>] (do_init_module) from [<c01c8a3c>] (SyS_finit_module+0x88/0x90)
>>> [ 5.897313] [<c01c8a3c>] (SyS_finit_module) from [<c0107120>] (ret_fast_syscall+0x0/0x1c)
>>> [ 5.912697] ------------[ cut here ]------------
>>> [ 5.912711] WARNING: CPU: 0 PID: 994 at kernel/sched/core.c:2996 _raw_spin_unlock+0x28/0x58
>>> [ 5.912717] DEBUG_LOCKS_WARN_ON(val > preempt_count())
>>>
>>> A liitle analysis of the code shows me:
>>>
>>> * udevd tries to initialize some (usb driver?) module
>>> * this calls usbhs_runtime_resume: http://lxr.free-electrons.com/source/drivers/mfd/omap-usb-host.c#L310
>>> * which calls omap_tll_enable: http://lxr.free-electrons.com/source/drivers/mfd/omap-usb-tll.c#L403
>>> * this does a spinlock: http://lxr.free-electrons.com/source/drivers/mfd/omap-usb-tll.c#L413
>>> * but calls clk_prepare_enable: http://lxr.free-electrons.com/source/include/linux/clk.h#L467
>>> * which calls: http://lxr.free-electrons.com/source/drivers/clk/clk.c#L658
>>> * and there is a another lock being tried in clk_prepare_lock: http://lxr.free-electrons.com/source/drivers/clk/clk.c#L91
>>> * and that is a mutex_try_lock
>>>
>>> So the lock dependency report is very valid. Inside a spinlock, there is a mutex_try_lock.
>>>
>>> It appears as if the spinlock was introduced in 2008 by 76a0775d46da052f123b8598a3dfc3b330b8de4f
>>> And the mutex in 2013 by 533ddeb1e86f506129ee388a6cc13796dcf31311
>>>
>>> Please fix.
>>>
>>> Thank you,
>>> Nikolaus
>>
>> Does this patch fix it for you?
>>
>> --
>> cheers,
>> -roger
>>
>> diff --git a/drivers/mfd/omap-usb-tll.c b/drivers/mfd/omap-usb-tll.c
>> index b7b3e8e..c30290f 100644
>> --- a/drivers/mfd/omap-usb-tll.c
>> +++ b/drivers/mfd/omap-usb-tll.c
>> @@ -269,6 +269,8 @@ static int usbtll_omap_probe(struct platform_device *pdev)
>>
>> if (IS_ERR(tll->ch_clk[i]))
>> dev_dbg(dev, "can't get clock : %s\n", clkname);
>> + else
>> + clk_prepare(tll->ch_clk[i]);
>> }
>>
>> pm_runtime_put_sync(dev);
>> @@ -301,9 +303,12 @@ static int usbtll_omap_remove(struct platform_device *pdev)
>> tll_dev = NULL;
>> spin_unlock(&tll_lock);
>>
>> - for (i = 0; i < tll->nch; i++)
>> - if (!IS_ERR(tll->ch_clk[i]))
>> + for (i = 0; i < tll->nch; i++) {
>> + if (!IS_ERR(tll->ch_clk[i])) {
>> + clk_unprepare(tll->ch_clk[i]);
>> clk_put(tll->ch_clk[i]);
>> + }
>> + }
>>
>> pm_runtime_disable(&pdev->dev);
>> return 0;
>> @@ -420,7 +425,7 @@ int omap_tll_enable(struct usbhs_omap_platform_data *pdata)
>> if (IS_ERR(tll->ch_clk[i]))
>> continue;
>>
>> - r = clk_prepare_enable(tll->ch_clk[i]);
>> + r = clk_enable(tll->ch_clk[i]);
>> if (r) {
>> dev_err(tll_dev,
>> "Error enabling ch %d clock: %d\n", i, r);
>> @@ -448,7 +453,7 @@ int omap_tll_disable(struct usbhs_omap_platform_data *pdata)
>> for (i = 0; i < tll->nch; i++) {
>> if (omap_usb_mode_needs_tll(pdata->port_mode[i])) {
>> if (!IS_ERR(tll->ch_clk[i]))
>> - clk_disable_unprepare(tll->ch_clk[i]);
>> + clk_disable(tll->ch_clk[i]);
>> }
>> }
>
> I will give it a try. Since it is sporadic I can tell only after some days of use if it did not happen any more.

I have it in my tree for a while and did no longer observe the BUG.
And I did not experience side effects (e.g. usb not working...).

So I think it works and solves the issue.

BR and thanks,
Nikolaus

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