Re: [PATCH v2 2/6] rcu-tasks: Add data to eliminate RCU-tasks/do_exit() deadlocks

Frederic Weisbecker
2024-02-22T16:54:51Z

Le Fri, Feb 16, 2024 at 05:27:37PM -0800, Boqun Feng a écrit :
> From: "Paul E. McKenney" <paulmck@kernel.org>
>
> Holding a mutex across synchronize_rcu_tasks() and acquiring
> that same mutex in code called from do_exit() after its call to
> exit_tasks_rcu_start() but before its call to exit_tasks_rcu_stop()
> results in deadlock. This is by design, because tasks that are far
> enough into do_exit() are no longer present on the tasks list, making
> it a bit difficult for RCU Tasks to find them, let alone wait on them
> to do a voluntary context switch. However, such deadlocks are becoming
> more frequent. In addition, lockdep currently does not detect such
> deadlocks and they can be difficult to reproduce.
>
> In addition, if a task voluntarily context switches during that time
> (for example, if it blocks acquiring a mutex), then this task is in an
> RCU Tasks quiescent state. And with some adjustments, RCU Tasks could
> just as well take advantage of that fact.
>
> This commit therefore adds the data structures that will be needed
> to rely on these quiescent states and to eliminate these deadlocks.
>
> Link: https://lore.kernel.org/all/20240118021842.290665-1-chenzhongjin@huawei.com/
>
> Reported-by: Chen Zhongjin <chenzhongjin@huawei.com>
> Reported-by: Yang Jihong <yangjihong1@huawei.com>
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> Tested-by: Yang Jihong <yangjihong1@huawei.com>
> Tested-by: Chen Zhongjin <chenzhongjin@huawei.com>
> Signed-off-by: Boqun Feng <boqun.feng@gmail.com>

Reviewed-by: Frederic Weisbecker <frederic@kernel.org>