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/fs/exec.c b/fs/exec.c
index 966c5c5..be923e4 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -760,7 +760,7 @@
*/
read_lock(&tasklist_lock);
spin_lock_irq(lock);
- if (sig->flags & SIGNAL_GROUP_EXIT) {
+ if (signal_group_exit(sig)) {
/*
* Another group action in progress, just
* return so that the signal is processed.
@@ -778,6 +778,7 @@
if (unlikely(tsk->group_leader == task_child_reaper(tsk)))
task_active_pid_ns(tsk)->child_reaper = tsk;
+ sig->group_exit_task = tsk;
zap_other_threads(tsk);
read_unlock(&tasklist_lock);
@@ -802,7 +803,6 @@
}
sig->notify_count = count;
- sig->group_exit_task = tsk;
while (atomic_read(&sig->count) > count) {
__set_current_state(TASK_UNINTERRUPTIBLE);
spin_unlock_irq(lock);
@@ -871,15 +871,10 @@
leader->exit_state = EXIT_DEAD;
write_unlock_irq(&tasklist_lock);
- }
+ }
sig->group_exit_task = NULL;
sig->notify_count = 0;
- /*
- * There may be one thread left which is just exiting,
- * but it's safe to stop telling the group to kill themselves.
- */
- sig->flags = 0;
no_thread_group:
exit_itimers(sig);
@@ -1549,7 +1544,7 @@
int err = -EAGAIN;
spin_lock_irq(&tsk->sighand->siglock);
- if (!(tsk->signal->flags & SIGNAL_GROUP_EXIT)) {
+ if (!signal_group_exit(tsk->signal)) {
tsk->signal->group_exit_code = exit_code;
zap_process(tsk);
err = 0;