exec: RT sub-thread can livelock and monopolize CPU on exec
de_thread() yields waiting for ->group_leader to be a zombie. This deadlocks
if an rt-prio execer shares the same cpu with ->group_leader. Change the code
to use ->group_exit_task/notify_count mechanics.
This patch certainly uglifies the code, perhaps someone can suggest something
better.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/exit.c b/kernel/exit.c
index 25f6805..4c108df 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -92,10 +92,9 @@
* If there is any task waiting for the group exit
* then notify it:
*/
- if (sig->group_exit_task && atomic_read(&sig->count) == sig->notify_count) {
+ if (sig->group_exit_task && atomic_read(&sig->count) == sig->notify_count)
wake_up_process(sig->group_exit_task);
- sig->group_exit_task = NULL;
- }
+
if (tsk == sig->curr_target)
sig->curr_target = next_thread(tsk);
/*
@@ -827,6 +826,11 @@
state = EXIT_DEAD;
tsk->exit_state = state;
+ if (thread_group_leader(tsk) &&
+ tsk->signal->notify_count < 0 &&
+ tsk->signal->group_exit_task)
+ wake_up_process(tsk->signal->group_exit_task);
+
write_unlock_irq(&tasklist_lock);
list_for_each_safe(_p, _n, &ptrace_dead) {