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" <ebiederm@xxxxxxxxxxxx>
---
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
