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Commit d5bbd43d authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
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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: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b5356a19

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 @@ static int de_thread(struct task_struct *tsk) 


	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)