On Fri, Sep 11, 2009 at 2:10 PM, Kevin
Hilman<khilman@xxxxxxxxxxxxxxxxxxx> wrote:
> Mike Turquette <mturquette@xxxxxx> writes:
>
>> Kevin Hilman wrote:
>>> Mike Chan <mike@xxxxxxxxxxx> writes:
>>>
>>>> Need to lock the res_mutex when traversing the res_list.
>>>>
>>>> Signed-off-by: Mike Chan <mike@xxxxxxxxxxx>
>>>
>>> Looks good, thanks.
>>
>> This patch causes a hang for me when transitioning to OFF mode. This
>> was tested on the Android 2.6.29 tree and is 100% reproducible. The
>> moment a user runs 'echo 1 > /sys/power/enable_off_mode' the board
>> hangs without any further output.
>>
>> Reverting the patch allows me to hit OFF mode again. I haven't yet
>> tested this on vanilla 2.6.29 or latest L-O.
>>
>
> OK, reverting this in both PM branches. Looks like a deadlock to me,
> as update_resource_level() must cause a call to something else that
> takes the mutex.
>
Good catch, I see the deadlock are in the change_level function
pointers. Where set_xxx will call resource_request() or
resource_release() => resource_lookup() which grabs the list mutex we
grabbed in resource_refresh().
Thoughts on changing the mutex to a RW semaphore?
-- Mike
> Kevin
>
>>
>>> Pushed to PM branch and pm-2.6.29.
>>>
>>> Kevin
>>>
>>>> ---
>>>> arch/arm/plat-omap/resource.c | 2 ++
>>>> 1 files changed, 2 insertions(+), 0 deletions(-)
>>>>
>>>> diff --git a/arch/arm/plat-omap/resource.c b/arch/arm/plat-omap/resource.c
>>>> index 25072cd..4631912 100644
>>>> --- a/arch/arm/plat-omap/resource.c
>>>> +++ b/arch/arm/plat-omap/resource.c
>>>> @@ -234,11 +234,13 @@ int resource_refresh(void)
>>>> struct shared_resource *resp = NULL;
>>>> int ret = 0;
>>>> + down(&res_mutex);
>>>> list_for_each_entry(resp, &res_list, node) {
>>>> ret = update_resource_level(resp);
>>>> if (ret)
>>>> break;
>>>> }
>>>> + up(&res_mutex);
>>>> return ret;
>>>> }
>>>> --
>>>> 1.5.4.5
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