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SubjectRe: [PATCH] [RFC] cpufreq: Avoid crash in resume on SMP without OPP
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On Tuesday, November 04, 2014 05:05:25 PM Geert Uytterhoeven wrote:
> When resuming from s2ram on an SMP system without cpufreq operating
> points (e.g. there's no "operating-points" property for the CPU node in
> DT, or the platform doesn't use DT yet), the kernel crashes when
> bringing CPU 1 online:
>
> Enabling non-boot CPUs ...
> CPU1: Booted secondary processor
> Unable to handle kernel NULL pointer dereference at virtual address 0000003c
> pgd = ee5e6b00
> [0000003c] *pgd=6e579003, *pmd=6e588003, *pte=00000000
> Internal error: Oops: a07 [#1] SMP ARM
> Modules linked in:
> CPU: 0 PID: 1246 Comm: s2ram Tainted: G W 3.18.0-rc3-koelsch-01614-g0377af242bb175c8-dirty #589
> task: eeec5240 ti: ee704000 task.ti: ee704000
> PC is at __cpufreq_add_dev.isra.24+0x24c/0x77c
> LR is at __cpufreq_add_dev.isra.24+0x244/0x77c
> pc : [<c0298efc>] lr : [<c0298ef4>] psr: 60000153
> sp : ee705d48 ip : ee705d48 fp : ee705d84
> r10: c04e0450 r9 : 00000000 r8 : 00000001
> r7 : c05426a8 r6 : 00000001 r5 : 00000001 r4 : 00000000
> r3 : 00000000 r2 : 00000000 r1 : 20000153 r0 : c0542734
>
> Verify that policy is not NULL before dereferencing it to fix this.
>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> ---
> Notes:
> - Is this the right fix?

The fix looks correct to me.

To my eyes what happens is that cpufreq_driver->init() in __cpufreq_add_dev()
fails and then cpufreq_cpu_data_fallback is cleared. cpufreq_cpu_data is not
set for the CPU, so cpufreq_cpu_data_fallback is NULL all the time. Then,
during resume, __cpufreq_add_dev() is called again and it calls
cpufreq_policy_restore(), because cpufreq_suspended is set. You know the rest. :-)

I'm queuing this up for the next PM pull request (most likely next week
for -rc5).

> - Interestingly, the crash is the same as the one reported in
> http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=c81407fe573d8ac3c7150f5373475598c59197de
> ("cpufreq: cpufreq-dt: Restore default cpumask_setall(policy->cpus)"),
> but the cause is different.
>
> - The crash was initially observed on sh73a0/kzm9g-legacy, but it can
> easily be reproduced on e.g. r8a7791/koelsch, by removing the
> "operating-points" property from the cpu0 node in
> arch/arm/boot/dts/r8a7791.dtsi, or by any other means to make the
> call to dev_pm_opp_init_cpufreq_table() in
> drivers/cpufreq/cpufreq-dt.c:cpufreq_init() fail.
>
> - I did not add
>
> Fixes: 6e2c89d16d987e6e ("cpufreq: move call to __find_governor() to cpufreq_init_policy()")

To me, that should be:

Fixes: 8414809c6a1e (cpufreq: Preserve policy structure across suspend/resume)

and therefore should go into 3.12+.

I'll add the appropriate tags.

>
> as I couldn't verify that the issue is also present in that (old)
> version (there have been too many s2ram-related platform and driver
> fixes since v3.15).
> ---
> drivers/cpufreq/cpufreq.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 644b54e1e7d13e8e..4473eba1d6b0b608 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1022,7 +1022,8 @@ static struct cpufreq_policy *cpufreq_policy_restore(unsigned int cpu)
>
> read_unlock_irqrestore(&cpufreq_driver_lock, flags);
>
> - policy->governor = NULL;
> + if (policy)
> + policy->governor = NULL;
>
> return policy;
> }
>

--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.


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