exec: make de_thread() killable
Change de_thread() to use KILLABLE rather than UNINTERRUPTIBLE while
waiting for other threads. The only complication is that we should
clear ->group_exit_task and ->notify_count before we return, and we
should do this under tasklist_lock. -EAGAIN is used to match the
initial signal_group_exit() check/return, it doesn't really matter.
This fixes the (unlikely) race with coredump. de_thread() checks
signal_group_exit() before it starts to kill the subthreads, but this
can't help if another CLONE_VM (but non CLONE_THREAD) task starts the
coredumping after de_thread() unlocks ->siglock. In this case the
killed sub-thread can block in exit_mm() waiting for coredump_finish(),
execing thread waits for that sub-thead, and the coredumping thread
waits for execing thread. Deadlock.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/exec.c b/fs/exec.c
index 9824473..19f4fb8 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -878,9 +878,11 @@
sig->notify_count--;
while (sig->notify_count) {
- __set_current_state(TASK_UNINTERRUPTIBLE);
+ __set_current_state(TASK_KILLABLE);
spin_unlock_irq(lock);
schedule();
+ if (unlikely(__fatal_signal_pending(tsk)))
+ goto killed;
spin_lock_irq(lock);
}
spin_unlock_irq(lock);
@@ -898,9 +900,11 @@
write_lock_irq(&tasklist_lock);
if (likely(leader->exit_state))
break;
- __set_current_state(TASK_UNINTERRUPTIBLE);
+ __set_current_state(TASK_KILLABLE);
write_unlock_irq(&tasklist_lock);
schedule();
+ if (unlikely(__fatal_signal_pending(tsk)))
+ goto killed;
}
/*
@@ -994,6 +998,14 @@
BUG_ON(!thread_group_leader(tsk));
return 0;
+
+killed:
+ /* protects against exit_notify() and __exit_signal() */
+ read_lock(&tasklist_lock);
+ sig->group_exit_task = NULL;
+ sig->notify_count = 0;
+ read_unlock(&tasklist_lock);
+ return -EAGAIN;
}
char *get_task_comm(char *buf, struct task_struct *tsk)