Re: cpufreq + PREEMPT_RT_FULL give bad context sleeping BUG

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

* Gregoire Gentil | 2013-03-23 10:17:51 [-0700]:

>Hello,
Hi,

>On OMAP + 3.4 + rt patches with CONFIG_PREEMPT_RT_FULL
>CONFIG_CPU_FREQ_GOV_ONDEMAND, I get a lot of those cpufreq-related
>bugs:
>
>http://pastebin.com/csy9y3xk
>
>BUG: sleeping function called from invalid context at kernel/rtmutex.c:646
>(__might_sleep+0x124/0x144) from (rt_spin_lock+0x30/0x64)
>(rt_spin_lock+0x30/0x64) from (clk_get_rate+0x30/0x54)
>(clk_get_rate+0x30/0x54) from (twd_update_frequency+0x20/0x58)

Here it tries to grab a mutex

>(twd_update_frequency+0x20/0x58) from (smp_call_function_single+0xd0/0x1c4)
>(smp_call_function_single+0xd0/0x1c4) from

Here it calls a smp functions which runs with interupts off.

>(twd_cpufreq_transition+0x34/0x40)

that means it should trigger on mainline as well.

>Any idea what I should do to fix this problem?

This has been introduced in 4fd7f9b12 ("ARM: 7212/1: smp_twd: reconfigure
clockevents after cpufreq change"). I think that omap got later
converted to the generic clk framework which uses now the mutex. Could
somebody please look at this?

>Grégoire

Sebastian
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