From 5dee1707dfbfc55eb7569b9ae5abaf932bd4c377 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Fri, 8 Feb 2008 04:19:13 -0800 Subject: move the related code from exit_notify() to exit_signals() The previous bugfix was not optimal, we shouldn't care about group stop when we are the only thread or the group stop is in progress. In that case nothing special is needed, just set PF_EXITING and return. Also, take the related "TIF_SIGPENDING re-targeting" code from exit_notify(). So, from the performance POV the only difference is that we don't trust !signal_pending() until we take ->siglock. But this in fact fixes another ___pure___ theoretical minor race. __group_complete_signal() finds the task without PF_EXITING and chooses it as the target for signal_wake_up(). But nothing prevents this task from exiting in between without noticing the pending signal and thus unpredictably delaying the actual delivery. Signed-off-by: Oleg Nesterov Cc: Davide Libenzi Cc: Ingo Molnar Cc: Roland McGrath Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/signal.c | 27 ++++++++++++++++++++++----- 1 file changed, 22 insertions(+), 5 deletions(-) (limited to 'kernel/signal.c') diff --git a/kernel/signal.c b/kernel/signal.c index 209eec11eef..3d3adb94561 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -1903,19 +1903,36 @@ relock: void exit_signals(struct task_struct *tsk) { int group_stop = 0; + struct task_struct *t; - 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; + if (thread_group_empty(tsk) || signal_group_exit(tsk->signal)) { + tsk->flags |= PF_EXITING; + return; } + spin_lock_irq(&tsk->sighand->siglock); /* * From now this task is not visible for group-wide signals, * see wants_signal(), do_signal_stop(). */ tsk->flags |= PF_EXITING; + if (!signal_pending(tsk)) + goto out; + + /* It could be that __group_complete_signal() choose us to + * notify about group-wide signal. Another thread should be + * woken now to take the signal since we will not. + */ + for (t = tsk; (t = next_thread(t)) != tsk; ) + if (!signal_pending(t) && !(t->flags & PF_EXITING)) + recalc_sigpending_and_wake(t); + + if (unlikely(tsk->signal->group_stop_count) && + !--tsk->signal->group_stop_count) { + tsk->signal->flags = SIGNAL_STOP_STOPPED; + group_stop = 1; + } +out: spin_unlock_irq(&tsk->sighand->siglock); if (unlikely(group_stop)) { -- cgit v1.2.3