policy->rwsem is used to lock access to all parts of code modifying struct cpufreq_policy but wasn't used on a new policy created from __cpufreq_add_dev().
Because of which if we call cpufreq_update_policy() repeatedly on one CPU and do offline/online of another CPU then we might see these crashes:
Unable to handle kernel NULL pointer dereference at virtual address 00000020 pgd = c0003000 [00000020] *pgd=80000000004003, *pmd=00000000 Internal error: Oops: 206 [#1] PREEMPT SMP ARM
PC is at __cpufreq_governor+0x10/0x1ac LR is at cpufreq_update_policy+0x114/0x150
---[ end trace f23a8defea6cd706 ]--- Kernel panic - not syncing: Fatal exception CPU0: stopping CPU: 0 PID: 7136 Comm: mpdecision Tainted: G D W 3.10.0-gd727407-00074-g979ede8 #396
[<c0afe180>] (notifier_call_chain+0x40/0x68) from [<c02a23ac>] (__blocking_notifier_call_chain+0x40/0x58) [<c02a23ac>] (__blocking_notifier_call_chain+0x40/0x58) from [<c02a23d8>] (blocking_notifier_call_chain+0x14/0x1c) [<c02a23d8>] (blocking_notifier_call_chain+0x14/0x1c) from [<c0803c68>] (cpufreq_set_policy+0xd4/0x2b8) [<c0803c68>] (cpufreq_set_policy+0xd4/0x2b8) from [<c0803e7c>] (cpufreq_init_policy+0x30/0x98) [<c0803e7c>] (cpufreq_init_policy+0x30/0x98) from [<c0805a18>] (__cpufreq_add_dev.isra.17+0x4dc/0x7a4) [<c0805a18>] (__cpufreq_add_dev.isra.17+0x4dc/0x7a4) from [<c0805d38>] (cpufreq_cpu_callback+0x58/0x84) [<c0805d38>] (cpufreq_cpu_callback+0x58/0x84) from [<c0afe180>] (notifier_call_chain+0x40/0x68) [<c0afe180>] (notifier_call_chain+0x40/0x68) from [<c02812dc>] (__cpu_notify+0x28/0x44) [<c02812dc>] (__cpu_notify+0x28/0x44) from [<c0aeed90>] (_cpu_up+0xf4/0x1dc) [<c0aeed90>] (_cpu_up+0xf4/0x1dc) from [<c0aeeed4>] (cpu_up+0x5c/0x78) [<c0aeeed4>] (cpu_up+0x5c/0x78) from [<c0aec808>] (store_online+0x44/0x74) [<c0aec808>] (store_online+0x44/0x74) from [<c03a40f4>] (sysfs_write_file+0x108/0x14c) [<c03a40f4>] (sysfs_write_file+0x108/0x14c) from [<c03517d4>] (vfs_write+0xd0/0x180) [<c03517d4>] (vfs_write+0xd0/0x180) from [<c0351ca8>] (SyS_write+0x38/0x68) [<c0351ca8>] (SyS_write+0x38/0x68) from [<c0205de0>] (ret_fast_syscall+0x0/0x30)
Fix these by taking locks at appropriate places in __cpufreq_add_dev() as well.
Reported-by: Saravana Kannan skannan@codeaurora.org Suggested-by: Srivatsa S. Bhat srivatsa.bhat@linux.vnet.ibm.com Signed-off-by: Viresh Kumar viresh.kumar@linaro.org --- drivers/cpufreq/cpufreq.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index 110c0cd..513d1d4 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -1130,6 +1130,7 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif, policy->user_policy.max = policy->max; }
+ down_write(&policy->rwsem); write_lock_irqsave(&cpufreq_driver_lock, flags); for_each_cpu(j, policy->cpus) per_cpu(cpufreq_cpu_data, j) = policy; @@ -1204,6 +1205,7 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif, policy->user_policy.policy = policy->policy; policy->user_policy.governor = policy->governor; } + up_write(&policy->rwsem);
kobject_uevent(&policy->kobj, KOBJ_ADD); up_read(&cpufreq_rwsem);