exec: rework the group exit and fix the race with kill
As Roland pointed out, we have the very old problem with exec. de_thread()
sets SIGNAL_GROUP_EXIT, kills other threads, changes ->group_leader and then
clears signal->flags. All signals (even fatal ones) sent in this window
(which is not too small) will be lost.
With this patch exec doesn't abuse SIGNAL_GROUP_EXIT. signal_group_exit(),
the new helper, should be used to detect exit_group() or exec() in progress.
It can have more users, but this patch does only strictly necessary changes.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Robin Holt <holt@sgi.com>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/exit.c b/kernel/exit.c
index 9e459fe..9d3d0f0 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1083,11 +1083,12 @@
struct signal_struct *const sig = current->signal;
struct sighand_struct *const sighand = current->sighand;
spin_lock_irq(&sighand->siglock);
- if (sig->flags & SIGNAL_GROUP_EXIT)
+ if (signal_group_exit(sig))
/* Another thread got here before we took the lock. */
exit_code = sig->group_exit_code;
else {
sig->group_exit_code = exit_code;
+ sig->flags = SIGNAL_GROUP_EXIT;
zap_other_threads(current);
}
spin_unlock_irq(&sighand->siglock);
diff --git a/kernel/signal.c b/kernel/signal.c
index 1117b28..6a5f97c 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -957,7 +957,6 @@
{
struct task_struct *t;
- p->signal->flags = SIGNAL_GROUP_EXIT;
p->signal->group_stop_count = 0;
for (t = next_thread(p); t != p; t = next_thread(t)) {
@@ -1697,7 +1696,8 @@
} else {
struct task_struct *t;
- if (!likely(sig->flags & SIGNAL_STOP_DEQUEUED))
+ if (!likely(sig->flags & SIGNAL_STOP_DEQUEUED) ||
+ unlikely(sig->group_exit_task))
return 0;
/*
* There is no group stop already in progress.
