[Starpu-devel] A possible bug in StarPU 1.3.xx

[Mirko Myllykoski <mirkom@cs.umu.se>]

Hi,

I believe that I have found a bug from StarPU 1.3.xx. I am
trying to create a scheduling context that contains a set of
CPU and CUDA workers. The code functions perfectly with
StarPU 1.2.6 but leads to a segmentation fault with StarPU
1.3.xx. I have isolated the problem to the following code
lines:

========== CODE BEGINS ==========

#include <starpu.h>

int main()
{
    if (starpu_init(NULL) != 0)
        abort();

    // get CPU workers
    int cpu_worker_ids[STARPU_NMAXWORKERS];
    int cpu_worker_count = starpu_worker_get_ids_by_type(
        STARPU_CPU_WORKER, cpu_worker_ids, STARPU_NMAXWORKERS);

    // get CUDA workers
    int gpu_worker_ids[STARPU_NMAXWORKERS];
    int gpu_worker_count = starpu_worker_get_ids_by_type(
        STARPU_CUDA_WORKER, gpu_worker_ids, STARPU_NMAXWORKERS);

    // create a parallel scheduling context and add all CPU
    // workers to it
    unsigned parallel_ctx = starpu_sched_ctx_create(
        cpu_worker_ids, cpu_worker_count, "parallel_cxt",
        STARPU_SCHED_CTX_POLICY_NAME, "pheft", 0);

    // add CUDA workers, if any, to the parallel scheduling
    // context
    if (0 < gpu_worker_count)
        starpu_sched_ctx_add_workers(   // <=== *** LINE 21 ***
            gpu_worker_ids, gpu_worker_count, parallel_ctx);

    starpu_sched_ctx_delete(parallel_ctx);
    starpu_shutdown();
}

==========  CODE ENDS  ==========

GDB backtrace:

========== GDB BEGINS  ==========

(gdb) bt
#0  0x00007ffff7846d29 in lws_select_victim (ws=0x555555a14250, 
sched_ctx_id=0, workerid=3) at sched_policies/work_stealing_policy.c:773
#1  0x00007ffff7845ff8 in ws_pop_task (sched_ctx_id=0) at 
sched_policies/work_stealing_policy.c:567
#2  0x00007ffff782a2f0 in _starpu_pop_task (worker=0x7ffff7ba31c8 
<_starpu_config+5640>) at core/sched_policy.c:871
#3  0x00007ffff78629aa in _starpu_get_worker_task (worker=0x7ffff7ba31c8 
<_starpu_config+5640>, workerid=3, memnode=0) at 
drivers/driver_common/driver_common.c:377
#4  0x00007ffff7915750 in _starpu_cpu_driver_run_once 
(cpu_worker=0x7ffff7ba31c8 <_starpu_config+5640>) at 
drivers/cpu/driver_cpu.c:303
#5  0x00007ffff7915dd8 in _starpu_cpu_worker (arg=0x7ffff7ba31c8 
<_starpu_config+5640>) at drivers/cpu/driver_cpu.c:407
#6  0x00007ffff6f756db in start_thread (arg=0x7fffbbfff700) at 
pthread_create.c:463
#7  0x00007ffff74b288f in clone () at 
../sysdeps/unix/sysv/linux/x86_64/clone.S:95

==========  GDB ENDS   ==========

Or, if I set STARPU_SCHED=prio, I get:

========== GDB BEGINS  ==========

(gdb) bt
#0  0x00007ffff783c59e in _starpu_sched_ctx_list_remove_elt 
(list=0x7ffff7ba25f8 <_starpu_config+2616>, rm=0x5555558979c0) at 
core/sched_ctx_list.c:262
#1  0x00007ffff783c6ad in _starpu_sched_ctx_list_move 
(list=0x7ffff7ba25f8 <_starpu_config+2616>, sched_ctx=1, prio_to=1) at 
core/sched_ctx_list.c:293
#2  0x00007ffff78390d3 in set_priority_on_notified_workers 
(workers=0x7fffffffd9b0, nworkers=1, sched_ctx_id=1, priority=1) at 
core/sched_ctx.c:2099
#3  0x00007ffff78356d9 in add_notified_workers 
(workerids=0x7fffffffd9b0, nworkers=1, sched_ctx_id=1) at 
core/sched_ctx.c:1228
#4  0x00007ffff7835fe7 in starpu_sched_ctx_add_workers 
(workers_to_add=0x7fffffffd9b0, nworkers_to_add=1, sched_ctx_id=1) at 
core/sched_ctx.c:1316
#5  0x0000555555554a54 in main () at main.c:21

==========  GDB ENDS   ==========

Best Regards,
Mirko Myllykoski