条件跳转或移动取决于未初始化值(分段错误/ Fortran)

Question

我正面临着一个分段故障。因此，我决定使用valgrind。对于编译，我使用：

gfortran -fopenmp -g HECESE_openmp.f90

对于执行，我使用：

valgrind --track-origins=yes ./a.out

我得到的错误之一是“条件跳转或移动依赖于未初始化值”，然后是“未初始化值是由堆栈分配创建的”。你可以在下面看到它。

==13202== Conditional jump or move depends on uninitialised value(s)
==13202==    at 0x1159DC: __procedures_MOD_grad._omp_fn.4 (HECESE_openmp.f90:690)
==13202==    by 0x4C78E75: GOMP_parallel (in /usr/lib/x86_64-linux-gnu/libgomp.so.1.0.0)
==13202==    by 0x10BF25: __procedures_MOD_grad (HECESE_openmp.f90:660)
==13202==    by 0x1123FF: MAIN__ (HECESE_openmp.f90:1063)
==13202==    by 0x113E89: main (HECESE_openmp.f90:721)
==13202==  Uninitialised value was created by a stack allocation
==13202==    at 0x10B211: __procedures_MOD_grad (HECESE_openmp.f90:482)
==13202== 
==13202== Conditional jump or move depends on uninitialised value(s)
==13202==    at 0x1159E2: __procedures_MOD_grad._omp_fn.4 (HECESE_openmp.f90:690)
==13202==    by 0x4C78E75: GOMP_parallel (in /usr/lib/x86_64-linux-gnu/libgomp.so.1.0.0)
==13202==    by 0x10BF25: __procedures_MOD_grad (HECESE_openmp.f90:660)
==13202==    by 0x1123FF: MAIN__ (HECESE_openmp.f90:1063)
==13202==    by 0x113E89: main (HECESE_openmp.f90:721)
==13202==  Uninitialised value was created by a stack allocation
==13202==    at 0x10B211: __procedures_MOD_grad (HECESE_openmp.f90:482)
==13202== 
==13202== Jump to the invalid address stated on the next line
==13202==    at 0x0: ???
==13202==    by 0x4C7BD7A: ??? (in /usr/lib/x86_64-linux-gnu/libgomp.so.1.0.0)
==13202==    by 0x4C846A7: ??? (in /usr/lib/x86_64-linux-gnu/libgomp.so.1.0.0)
==13202==    by 0x4C8304C: ??? (in /usr/lib/x86_64-linux-gnu/libgomp.so.1.0.0)
==13202==    by 0x10BF25: __procedures_MOD_grad (HECESE_openmp.f90:660)
==13202==    by 0x1123FF: MAIN__ (HECESE_openmp.f90:1063)
==13202==    by 0x113E89: main (HECESE_openmp.f90:721)
==13202==  Address 0x0 is not stack'd, malloc'd or (recently) free'd

下面是我编译的代码：

       tasklist_GRAD(5)%f_ptr => u_prime_2 !5
       tasklist_GRAD(6)%f_ptr => taux_ !6
       tasklist_GRAD(7)%f_ptr => u_prime_gauche_2 !7 
       tasklist_GRAD(8)%f_ptr => u_prime_droite_2 !8
       tasklist_GRAD(9)%f_ptr => ax_droite_1 !9
       tasklist_GRAD(10)%f_ptr => ax_gauche_1 !10
       tasklist_GRAD(11)%f_ptr => ux_droite_1 !11
       tasklist_GRAD(12)%f_ptr => ux_gauche_1 !12
       tasklist_GRAD(13)%f_ptr => u_grad_x_2 !13
       tasklist_GRAD(14)%f_ptr => u_prime_gauche_3 !14 
       tasklist_GRAD(15)%f_ptr => u_prime_droite_3 !15
       tasklist_GRAD(16)%f_ptr => ax_droite_2 !16
       tasklist_GRAD(17)%f_ptr => ax_gauche_2 !17
       tasklist_GRAD(18)%f_ptr => ux_droite_2 !18
       tasklist_GRAD(19)%f_ptr => ux_gauche_2 !19
       tasklist_GRAD(20)%f_ptr => u_grad_x_3 !20

       
       !$OMP PARALLEL PRIVATE(num_thread,nthreads) &
       !$OMP SHARED(tasklist_GRAD,threads_list,threads_list_all,tasks_ready_master) &
       !$OMP SHARED(threads_list_part1,threads_list_part2,threads_list_part3)
       num_thread=OMP_GET_THREAD_NUM()
       nthreads=OMP_GET_NUM_THREADS()


       !Thread Application Master
       if (num_thread==1) then
          do ff=5,20
             if (associated(tasklist_GRAD(ff)%f_ptr) .eqv. .true.) then
                tasks_ready_master(ff) = tasklist_GRAD(ff) 
             end if
          end do

          do ff=5,20
             if (associated(tasks_ready_master(ff)%f_ptr) .eqv. .true.) then
                tasks_ready_master(ff)%state=STATE_READY
             end if
          end do
       end if


       !Thread Master 
       if (num_thread==0) then
          allocate(threads_list(nthreads-2))
          do ff=1,nthreads-2
             threads_list(ff)=ff+1
          end do


          do ff=5,20,nthreads-2
             if (tasks_ready_master(ff)%state==STATE_READY) then
                threads_list_all(ff:ff+nthreads-3)=threads_list(:)
             end if
          end do
          threads_list_part3=threads_list_all(5:20)
       end if
       !$OMP BARRIER
       !Threads workers
       do ff=5,20
          if (num_thread==threads_list_part3(ff-4)) then
             !$OMP TASK
             call tasks_ready_master(ff)%f_ptr(self,ww,pas,cpt ,nb_element,cpt1,dt,dx,p_element,u_prime,u_prime_moins,u_prime_plus,&
                  &taux,grad_x_u,grad_t_u,grad_x_f,grad_t_f,ax_plus,ax_moins,ux_plus,ux_moins,sm,flux,tab0,tab)
             !$OMP END TASK
          end if
       end do

       !$OMP END PARALLEL    

第690行是：if (tasks_ready_master(ff)%state==STATE_READY) then

对于已用列表：

    type(tcb),dimension(20)::tasklist_GRAD,tasks_ready_master
    integer,allocatable,dimension(:)::threads_list
    integer,dimension(30)::threads_list_all
    integer,dimension(3)::threads_list_part1
    integer::threads_list_part2    
    integer,dimension(16)::threads_list_part3 

我忽略了错误的来源。你能帮帮我吗？这是我第一次使用Valgrind，也是我第一次在这个网站上提问。

Answer 1

不幸的是，您已经将代码编辑为工作版本，这掩盖了问题所在。前面代码的相关部分如下：

           !Thread Master 
           if (num_thread==0) then
...
              threads_list_part3=threads_list_all(5:20)
           end if
 
           !Threads workers
           do ff=5,20
              if (num_thread==threads_list_part3(ff-4)) then

你有一个竞态条件。线程0执行括号中的块，但其他线程仍在运行，因此进入do循环，因此在主线程初始化threads_list_part3之前，非主线程可能会访问它。最简单的解决方法是使用屏障来确保非主线程等待主线程完成其工作。您可以显式执行此操作

               !Thread Master 
               if (num_thread==0) then
    ...
                  threads_list_part3=threads_list_all(5:20)
               end if
!$omp barrier     
               !Threads workers
               do ff=5,20
                  if (num_thread==threads_list_part3(ff-4)) then 

或隐式地通过工作共享构造，如!$omp single

!$omp single
               !Thread Master 
    ...
               threads_list_part3=threads_list_all(5:20)
!$omp end single     
               !Threads workers
               do ff=5,20
                  if (num_thread==threads_list_part3(ff-4)) then

就我个人而言，我更喜欢第二种形式。