[ag-automation] Linux timer hangs sometime and stops at 1ns

[Vijay Katoch]

Hi,
I have an embedded board with PowerPC 5200 running Realtime Linux with 
version 2.6.33 (OSADL).
My application is using one high resolution timer in Linux for alarms. 
This timer sometimes didn’t expire. The problem happens very rarely, it 
may go many months between each time it happens on a systems.
The timer is set by function timer_settime with absolute time.
I have done some interesting observations when the timer didn’t expire: 
- Function timer_gettime returns remaining time 1ns.
- Active timers are checked by displaying file /proc/timer_list and the 
timer_list didn’t show this timer in the active timer list. 
I have looked into the Linux source and found a possible scenario:
The function timer_gettime ends up in function common_timer_get 
(posix-timers.c).  Function common_timer_get returns it_value.tv_nsec = 1 
if timer is active and remaining time is <= 0. This means that the timer 
has counted down and the timer state must be 'enqueued' or 'callback'.
I suppose that it is in state 'callback', that means it is running in 
function __run_hrtimer (hrtimer.c). Function __run_hrtimer is calling 
function__remove_hrtimer that remove the timer from timer active list 
before it changes timer state from 'enqueued' to 'callback'.
Several functions are called in function __run_hrtimer between changing 
timer state to 'callback' and the end of the function where the state 
'callback' is cleared.  If it is hanging here, the function timer_gettime 
may return 1ns while the timer is not in the active list. Here it is 
calling several functions in Linux kernel and the callback function in the 
application. 
I have checked the callback function in my application. It is signaling a 
semaphore and setting the timer again on the same thread. I can't see why 
that should not work. 
Is there someone that has seen a similar case?
Is there someone that has an idea of what are going wrong here?
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