From 6db840fa7887980ef68a649640d506fe069eef0c Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Tue, 16 Oct 2007 23:27:23 -0700 Subject: 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 Cc: Roland McGrath Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/exec.c | 28 +++++++++++++++------------- kernel/exit.c | 10 +++++++--- 2 files changed, 22 insertions(+), 16 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index ab5a4a3ece46..aa470a93540a 100644 --- a/fs/exec.c +++ b/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. diff --git a/kernel/exit.c b/kernel/exit.c index 25f6805be5fe..4c108df88a37 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -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) { -- cgit v1.2.3