Hi Oleg, Oleg Nesterov (oleg@xxxxxxxxxx) wrote: > On 01/06, Mandeep Singh Baines wrote: > > > > Oleg Nesterov (oleg@xxxxxxxxxx) wrote: > > > > > > > > in particular, http://marc.info/?l=linux-kernel&m=127714242731448 > > > > > I think this should work, but then we should do something with the > > > > > users like zap_threads(). > > > > > > > > > > > > > With that patch, won't you potentially miss the exec thread if an exec > > > > occurs while you're iterating over the list? Is that OK? > > > > > > Of course it is not OK ;) Note the "we should do something with" above. > > > > > > > So requirements should be something like this: > > (I assume, you mean the lockless case) > Correct. > > * Any task alive for the duration of the iteration MUST be visited > > * No task should be visited more than once > > * Any task born or exiting after starting the iteration MAY be skipped > > * You can start at any task in the thread group > > Well yes, but it is not easy to exactly define what after/before > means in this case. > > > Would something like this work: > > > > #define while_each_thread(g, t, o) \ > > while (t->group_leader == o && (t = next_thread(t)) != g) > > > > Where o should have the value of g->group_leader. > > I don't understand how this helps... and how this can work even > ignoring the barriers. > > OK, we have the main thream M and the sub-thread T, we are doing > > do { > do_something(t); > } while_each_thread(M, t, M); > > why we can't miss T if it does exec? > So for: struct task *M; /* assuming this is passed in to us */ struct task *L = M->group_leader; struct task *I = M; do { do_something(T); } while_each_thread(M, T, L); Here is my thinking. If some thread K does exec, you won't miss it because: 1) Ignoring the group_leader check, you'll visit K just by following next_thread(). That's the case today and is what you except when iterating over an rcu_list. 2) (t->group_leader == o) will fail iff t is the exec thread. Since we test t->group_leader before re-assigning it (t=next_thread()), the test will fail only after visiting the exec thread. So you'll visit the exec thread and then terminate the loop. I realize its a klutzy interface (requires 3 variables) but it seems correct (ignoring barriers) and meets all the requirements. I'm hoping it inspires a solution which is less klutzy and meet its all the requirements. Regards, Mandeep > Oleg. > _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers