On Tuesday, March 04, 2014 11:44:01 AM Viresh Kumar wrote: > 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@xxxxxxxxxxxxxx> > Suggested-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx> > Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx> I've rebased this one on top of 3.14-rc5 and queued it up for 3.14-rc6. Please check the bleeding-edge branch for the result. > --- > V1->V2: No change > > drivers/cpufreq/cpufreq.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > index 3c6f9a5..e2a1e67 100644 > --- a/drivers/cpufreq/cpufreq.c > +++ b/drivers/cpufreq/cpufreq.c > @@ -1128,6 +1128,7 @@ 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; > @@ -1202,6 +1203,7 @@ 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); > -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
