When taking the task_list_lock in de_thread also take the siglock. This makes de_thread closer to fork the canonical place where these locks are taken.
To complete the defensiveness always take siglock when clearing group_exit_task and notify_count. This gives now gives the guarantee that group_exit_task and notify_count are now always changed under siglock. As anything multi-threaded in exec is a rare and slow path I don't think we care if we take an extra lock in practice. The practical reason for doing this is to enable setting signal->flags along with group_exit_task so that the function signal_group_exit can be simplified. Signed-off-by: "Eric W. Biederman" <[email protected]> --- fs/exec.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index e6e8a9a70327..33b5d9229c01 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1171,6 +1171,7 @@ static int de_thread(struct task_struct *tsk) for (;;) { cgroup_threadgroup_change_begin(tsk); write_lock_irq(&tasklist_lock); + spin_lock(lock); /* * Do this under tasklist_lock to ensure that * exit_notify() can't miss ->group_exit_task @@ -1179,6 +1180,7 @@ static int de_thread(struct task_struct *tsk) if (likely(leader->exit_state)) break; __set_current_state(TASK_KILLABLE); + spin_unlock(lock); write_unlock_irq(&tasklist_lock); cgroup_threadgroup_change_end(tsk); schedule(); @@ -1234,14 +1236,17 @@ static int de_thread(struct task_struct *tsk) */ if (unlikely(leader->ptrace)) __wake_up_parent(leader, leader->parent); + spin_unlock(lock); write_unlock_irq(&tasklist_lock); cgroup_threadgroup_change_end(tsk); release_task(leader); } + spin_lock_irq(lock); sig->group_exit_task = NULL; sig->notify_count = 0; + spin_unlock_irq(lock); no_thread_group: /* we have changed execution domain */ @@ -1252,10 +1257,12 @@ static int de_thread(struct task_struct *tsk) killed: /* protects against exit_notify() and __exit_signal() */ - read_lock(&tasklist_lock); + read_lock_irq(&tasklist_lock); + spin_lock(lock); sig->group_exit_task = NULL; sig->notify_count = 0; - read_unlock(&tasklist_lock); + spin_unlock(lock); + read_unlock_irq(&tasklist_lock); return -EAGAIN; } -- 2.20.1
