exec: make de_thread() killable (d5bbd43d) · Commits · 戴 / test

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>

fs/exec.c

+14 −2

Original line number	Diff line number	Diff line
		@@ -878,9 +878,11 @@ static int de_thread(struct task_struct *tsk)
		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 @@ static int de_thread(struct task_struct *tsk)
		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 @@ no_thread_group:

		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)

Admin message