On Tue, 9 Feb 2010, Amerigo Wang wrote:
> Benjamin reported that, the machine deadlocks right after printing the
> following when doing a shutdown:
>
> halt/4071 is trying to acquire lock:
> (s_active){++++.+}, at: [<c0000000001ef868>] .sysfs_addrm_finish+0x58/0xc0
>
> but task is already holding lock:
> (&per_cpu(cpu_policy_rwsem, cpu)){+.+.+.}, at: [<c0000000004cd6ac>] .lock_policy_rwsem_write+0x84/0xf4
>
> which lock already depends on the new lock.
>
> the existing dependency chain (in reverse order) is:
>
> <nothing else ... machine deadlocked here>
>
>
> This is because we are trying to kobject_put() a kobject while
> we are holding cpu policy rwsem. So just move kobject_put()
> down after releasing the rwsem.
>
> Totally untested.
>
> Reported-by: Xiaotian Feng <xtfeng@xxxxxxxxx>
> Reported-by: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: WANG Cong <amwang@xxxxxxxxxx>
> Cc: Dave Jones <davej@xxxxxxxxxx>
> Cc: Thomas Renninger <trenn@xxxxxxx>
> Cc: Prarit Bhargava <prarit@xxxxxxxxxx>
> Cc: Venkatesh Pallipadi <venkatesh.pallipadi@xxxxxxxxx>
>
> ---
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 67bc2ec..222b35f 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1113,6 +1113,7 @@ static int __cpufreq_remove_dev(struct sys_device *sys_dev)
> unsigned int cpu = sys_dev->id;
> unsigned long flags;
> struct cpufreq_policy *data;
> + struct kobject *kobj;
> #ifdef CONFIG_SMP
> struct sys_device *cpu_sys_dev;
> unsigned int j;
> @@ -1192,7 +1193,7 @@ static int __cpufreq_remove_dev(struct sys_device *sys_dev)
> if (cpufreq_driver->target)
> __cpufreq_governor(data, CPUFREQ_GOV_STOP);
>
> - kobject_put(&data->kobj);
> + kobj = &data->kobj;
>
> /* we need to make sure that the underlying kobj is actually
> * not referenced anymore by anybody before we proceed with
NACK.
If you read this comment, it says:
/* we need to make sure that the underlying kobj is actually
* not referenced anymore by anybody before we proceed with
* unloading.
*/
That would suggest that the wait_for_completion(&data->kobj_unregister);
would never actually return if you're holding a reference to it in your
patch since it only completes when the last reference is dropped (the
->release function is cpufreq_sysfs_release()).
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