Synchronization problem in message queue mechanism

Cezar Antohe antohecezar at
Fri Aug 23 08:24:57 UTC 2013


Thanks a lot for the posting, I think what you have simulated there is exactly one of our problem manifestations. Indeed, after that pointer is NULL in _Thread_queue_Process_timeout, the system state is invalid and probably other bad manifestations we've seen, start to appear.

One question, please, if it's ok with you - for a fast fix, what would you suggest, either verify that pointer for NULL and return immediately, if it's invalid, or wait for a fixing patch from you guys ?
Or maybe disable interrupts altogether during the function call duration ? Would the NULL verification / interrupt disabling have negative impacts elsewhere ?
Again, we are no experts in RTEMS, so sorry if my questions may not seem valid.

Thanks a lot, cheers,

 From: Sebastian Huber <sebastian.huber at>
To: rtems-users at 
Sent: Thursday, August 22, 2013 6:37 PM
Subject: Re: Synchronization problem in message queue mechanism


for a test case please have a look at the attached patch.  If I run this test 
on a simulator I get:

(gdb) b threadqprocesstimeout.c:42 if the_thread_queue == 0
Breakpoint 3 at 0x201da00: file 
line 42.
(gdb) r
Starting program: 


Support - rtems_timer_create - creating timer 1

Breakpoint 3, _Thread_queue_Process_timeout (the_thread=0x2046b00) at 
42        if ( the_thread_queue->sync_state != 
(gdb) p the_thread_queue
$1 = (Thread_queue_Control *) 0x0

So we have a NULL pointer access in _Thread_queue_Process_timeout().  This 
destroys the system state.

On real systems the sequence in the test case can happen with nested interrupts 
which interrupt the clock tick handler (this is a common setup).

Sebastian Huber, embedded brains GmbH

Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone   : +49 89 189 47 41-16
Fax     : +49 89 189 47 41-09
E-Mail  : sebastian.huber at
PGP     : Public key available on request.

Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.

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