David Rientjes wrote:
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()).
Oh, my bad.
Then this case seems to be more complex... But anyway, this is _not_ a
bogus.
Thanks.
--
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
