From 5dee1707dfbfc55eb7569b9ae5abaf932bd4c377 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Fri, 8 Feb 2008 04:19:13 -0800 Subject: [PATCH] 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/exit.c | 18 ------------------ kernel/signal.c | 27 ++++++++++++++++++++++----- 2 files changed, 22 insertions(+), 23 deletions(-) diff --git a/kernel/exit.c b/kernel/exit.c index 8f3bf53a5b4d..2b332d170327 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -745,24 +745,6 @@ static void exit_notify(struct task_struct *tsk) struct task_struct *t; struct pid *pgrp; - if (signal_pending(tsk) && !(tsk->signal->flags & SIGNAL_GROUP_EXIT) - && !thread_group_empty(tsk)) { - /* - * This occurs when there was a race between our exit - * syscall and a group signal choosing us as the one to - * wake up. It could be that we are the only thread - * alerted to check for pending signals, but another thread - * should be woken now to take the signal since we will not. - * Now we'll wake all the threads in the group just to make - * sure someone gets all the pending signals. - */ - spin_lock_irq(&tsk->sighand->siglock); - for (t = next_thread(tsk); t != tsk; t = next_thread(t)) - if (!signal_pending(t) && !(t->flags & PF_EXITING)) - recalc_sigpending_and_wake(t); - spin_unlock_irq(&tsk->sighand->siglock); - } - /* * This does two things: * diff --git a/kernel/signal.c b/kernel/signal.c index 209eec11eef5..3d3adb94561d 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -1903,19 +1903,36 @@ int get_signal_to_deliver(siginfo_t *info, struct k_sigaction *return_ka, 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)) {