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>
This commit is contained in:
Родитель
356d6d5058
Коммит
6db840fa78
28
fs/exec.c
28
fs/exec.c
|
@ -801,16 +801,15 @@ static int de_thread(struct task_struct *tsk)
|
|||
hrtimer_restart(&sig->real_timer);
|
||||
spin_lock_irq(lock);
|
||||
}
|
||||
|
||||
sig->notify_count = count;
|
||||
sig->group_exit_task = tsk;
|
||||
while (atomic_read(&sig->count) > count) {
|
||||
sig->group_exit_task = tsk;
|
||||
sig->notify_count = count;
|
||||
__set_current_state(TASK_UNINTERRUPTIBLE);
|
||||
spin_unlock_irq(lock);
|
||||
schedule();
|
||||
spin_lock_irq(lock);
|
||||
}
|
||||
sig->group_exit_task = NULL;
|
||||
sig->notify_count = 0;
|
||||
spin_unlock_irq(lock);
|
||||
|
||||
/*
|
||||
|
@ -819,14 +818,17 @@ static int de_thread(struct task_struct *tsk)
|
|||
* and to assume its PID:
|
||||
*/
|
||||
if (!thread_group_leader(tsk)) {
|
||||
/*
|
||||
* Wait for the thread group leader to be a zombie.
|
||||
* It should already be zombie at this point, most
|
||||
* of the time.
|
||||
*/
|
||||
leader = tsk->group_leader;
|
||||
while (leader->exit_state != EXIT_ZOMBIE)
|
||||
yield();
|
||||
|
||||
sig->notify_count = -1;
|
||||
for (;;) {
|
||||
write_lock_irq(&tasklist_lock);
|
||||
if (likely(leader->exit_state))
|
||||
break;
|
||||
__set_current_state(TASK_UNINTERRUPTIBLE);
|
||||
write_unlock_irq(&tasklist_lock);
|
||||
schedule();
|
||||
}
|
||||
|
||||
/*
|
||||
* The only record we have of the real-time age of a
|
||||
|
@ -840,8 +842,6 @@ static int de_thread(struct task_struct *tsk)
|
|||
*/
|
||||
tsk->start_time = leader->start_time;
|
||||
|
||||
write_lock_irq(&tasklist_lock);
|
||||
|
||||
BUG_ON(leader->tgid != tsk->tgid);
|
||||
BUG_ON(tsk->pid == tsk->tgid);
|
||||
/*
|
||||
|
@ -874,6 +874,8 @@ static int de_thread(struct task_struct *tsk)
|
|||
write_unlock_irq(&tasklist_lock);
|
||||
}
|
||||
|
||||
sig->group_exit_task = NULL;
|
||||
sig->notify_count = 0;
|
||||
/*
|
||||
* There may be one thread left which is just exiting,
|
||||
* but it's safe to stop telling the group to kill themselves.
|
||||
|
|
|
@ -92,10 +92,9 @@ static void __exit_signal(struct task_struct *tsk)
|
|||
* 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 @@ static void exit_notify(struct task_struct *tsk)
|
|||
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) {
|
||||
|
|
Загрузка…
Ссылка в новой задаче