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Subject[PATCH] [RFC] cpufreq: Avoid crash in resume on SMP without OPP
Date
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?

- 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()")

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;
}
--
1.9.1


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