From d12619b5ff5664623524aef796514d1946ea3b4a Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Fri, 8 Feb 2008 04:19:12 -0800 Subject: [PATCH] fix group stop with exit race do_signal_stop() counts all sub-thread and sets ->group_stop_count accordingly. Every thread should decrement ->group_stop_count and stop, the last one should notify the parent. However a sub-thread can exit before it notices the signal_pending(), or it may be somewhere in do_exit() already. In that case the group stop never finishes properly. Note: this is a minimal fix, we can add some optimizations later. Say we can return quickly if thread_group_empty(). Also, we can move some signal related code from exit_notify() to exit_signals(). Signed-off-by: Oleg Nesterov Acked-by: Davide Libenzi Cc: Ingo Molnar Cc: Roland McGrath Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/signal.h | 1 + kernel/exit.c | 2 +- kernel/signal.c | 27 ++++++++++++++++++++++++++- 3 files changed, 28 insertions(+), 2 deletions(-) diff --git a/include/linux/signal.h b/include/linux/signal.h index 7e095147656..42d2e0a948f 100644 --- a/include/linux/signal.h +++ b/include/linux/signal.h @@ -241,6 +241,7 @@ extern int show_unhandled_signals; struct pt_regs; extern int get_signal_to_deliver(siginfo_t *info, struct k_sigaction *return_ka, struct pt_regs *regs, void *cookie); +extern void exit_signals(struct task_struct *tsk); extern struct kmem_cache *sighand_cachep; diff --git a/kernel/exit.c b/kernel/exit.c index d7815f57088..8f3bf53a5b4 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -947,7 +947,7 @@ fastcall NORET_TYPE void do_exit(long code) schedule(); } - tsk->flags |= PF_EXITING; + exit_signals(tsk); /* sets PF_EXITING */ /* * tsk->flags are checked in the futex code to protect against * an exiting task cleaning up the robust pi futexes. diff --git a/kernel/signal.c b/kernel/signal.c index 3fca710a5cd..209eec11eef 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -1739,7 +1739,7 @@ static int do_signal_stop(int signr) * stop is always done with the siglock held, * so this check has no races. */ - if (!t->exit_state && + if (!(t->flags & PF_EXITING) && !task_is_stopped_or_traced(t)) { stop_count++; signal_wake_up(t, 0); @@ -1900,6 +1900,31 @@ relock: return signr; } +void exit_signals(struct task_struct *tsk) +{ + int group_stop = 0; + + spin_lock_irq(&tsk->sighand->siglock); + if (unlikely(tsk->signal->group_stop_count) && + !--tsk->signal->group_stop_count) { + tsk->signal->flags = SIGNAL_STOP_STOPPED; + group_stop = 1; + } + + /* + * From now this task is not visible for group-wide signals, + * see wants_signal(), do_signal_stop(). + */ + tsk->flags |= PF_EXITING; + spin_unlock_irq(&tsk->sighand->siglock); + + if (unlikely(group_stop)) { + read_lock(&tasklist_lock); + do_notify_parent_cldstop(tsk, CLD_STOPPED); + read_unlock(&tasklist_lock); + } +} + EXPORT_SYMBOL(recalc_sigpending); EXPORT_SYMBOL_GPL(dequeue_signal); EXPORT_SYMBOL(flush_signals); -- 2.41.1