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authorOleg Nesterov <oleg@tv-sign.ru>2008-04-30 03:52:44 -0400
committerLinus Torvalds <torvalds@linux-foundation.org>2008-04-30 11:29:34 -0400
commite442055193e4584218006e616c9bdce0c5e9ae5c (patch)
tree5e444253953c2f48c0a194bf8c5799f03bb2e266 /kernel
parent3b5e9e53c6f31b5a5a0f5c43707503c62bdefa46 (diff)
signals: re-assign CLD_CONTINUED notification from the sender to reciever
Based on discussion with Jiri and Roland. In short: currently handle_stop_signal(SIGCONT, p) sends the notification to p->parent, with this patch p itself notifies its parent when it becomes running. handle_stop_signal(SIGCONT) has to drop ->siglock temporary in order to notify the parent with do_notify_parent_cldstop(). This leads to multiple problems: - as Jiri Kosina pointed out, the stopped task can resume without actually seeing SIGCONT which may have a handler. - we race with another sig_kernel_stop() signal which may come in that window. - we race with sig_fatal() signals which may set SIGNAL_GROUP_EXIT in that window. - we can't avoid taking tasklist_lock() while sending SIGCONT. With this patch handle_stop_signal() just sets the new SIGNAL_CLD_CONTINUED flag in p->signal->flags and returns. The notification is sent by the first task which returns from finish_stop() (there should be at least one) or any other signalled thread from get_signal_to_deliver(). This is a user-visible change. Say, currently kill(SIGCONT, stopped_child) can't return without seeing SIGCHLD, with this patch SIGCHLD can be delayed unpredictably. Another difference is that if the child is ptraced by another process, CLD_CONTINUED may be delivered to ->real_parent after ptrace_detach() while currently it always goes to the tracer which doesn't actually need this notification. Hopefully not a problem. The patch asks for the futher obvious cleanups, I'll send them separately. Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Cc: Roland McGrath <roland@redhat.com> Cc: Jiri Kosina <jkosina@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/signal.c29
1 files changed, 19 insertions, 10 deletions
diff --git a/kernel/signal.c b/kernel/signal.c
index 91d57f89f5a5..115c04f3f143 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -603,10 +603,8 @@ static void handle_stop_signal(int sig, struct task_struct *p)
603 * the SIGCHLD was pending on entry to this kill. 603 * the SIGCHLD was pending on entry to this kill.
604 */ 604 */
605 p->signal->group_stop_count = 0; 605 p->signal->group_stop_count = 0;
606 p->signal->flags = SIGNAL_STOP_CONTINUED; 606 p->signal->flags = SIGNAL_STOP_CONTINUED |
607 spin_unlock(&p->sighand->siglock); 607 SIGNAL_CLD_STOPPED;
608 do_notify_parent_cldstop(p, CLD_STOPPED);
609 spin_lock(&p->sighand->siglock);
610 } 608 }
611 rm_from_queue(SIG_KERNEL_STOP_MASK, &p->signal->shared_pending); 609 rm_from_queue(SIG_KERNEL_STOP_MASK, &p->signal->shared_pending);
612 t = p; 610 t = p;
@@ -643,25 +641,23 @@ static void handle_stop_signal(int sig, struct task_struct *p)
643 * We were in fact stopped, and are now continued. 641 * We were in fact stopped, and are now continued.
644 * Notify the parent with CLD_CONTINUED. 642 * Notify the parent with CLD_CONTINUED.
645 */ 643 */
646 p->signal->flags = SIGNAL_STOP_CONTINUED; 644 p->signal->flags = SIGNAL_STOP_CONTINUED |
645 SIGNAL_CLD_CONTINUED;
647 p->signal->group_exit_code = 0; 646 p->signal->group_exit_code = 0;
648 spin_unlock(&p->sighand->siglock);
649 do_notify_parent_cldstop(p, CLD_CONTINUED);
650 spin_lock(&p->sighand->siglock);
651 } else { 647 } else {
652 /* 648 /*
653 * We are not stopped, but there could be a stop 649 * We are not stopped, but there could be a stop
654 * signal in the middle of being processed after 650 * signal in the middle of being processed after
655 * being removed from the queue. Clear that too. 651 * being removed from the queue. Clear that too.
656 */ 652 */
657 p->signal->flags = 0; 653 p->signal->flags &= ~SIGNAL_STOP_DEQUEUED;
658 } 654 }
659 } else if (sig == SIGKILL) { 655 } else if (sig == SIGKILL) {
660 /* 656 /*
661 * Make sure that any pending stop signal already dequeued 657 * Make sure that any pending stop signal already dequeued
662 * is undone by the wakeup for SIGKILL. 658 * is undone by the wakeup for SIGKILL.
663 */ 659 */
664 p->signal->flags = 0; 660 p->signal->flags &= ~SIGNAL_STOP_DEQUEUED;
665 } 661 }
666} 662}
667 663
@@ -1784,6 +1780,19 @@ relock:
1784 try_to_freeze(); 1780 try_to_freeze();
1785 1781
1786 spin_lock_irq(&current->sighand->siglock); 1782 spin_lock_irq(&current->sighand->siglock);
1783
1784 if (unlikely(current->signal->flags & SIGNAL_CLD_MASK)) {
1785 int why = (current->signal->flags & SIGNAL_STOP_CONTINUED)
1786 ? CLD_CONTINUED : CLD_STOPPED;
1787 current->signal->flags &= ~SIGNAL_CLD_MASK;
1788 spin_unlock_irq(&current->sighand->siglock);
1789
1790 read_lock(&tasklist_lock);
1791 do_notify_parent_cldstop(current->group_leader, why);
1792 read_unlock(&tasklist_lock);
1793 goto relock;
1794 }
1795
1787 for (;;) { 1796 for (;;) {
1788 struct k_sigaction *ka; 1797 struct k_sigaction *ka;
1789 1798