From 46faf9d8e1d52e4a91c382c6c72da6bd8e68297b Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 5 Feb 2024 13:10:19 -0800 Subject: rcu-tasks: Initialize data to eliminate RCU-tasks/do_exit() deadlocks 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 initializes 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 Reported-by: Yang Jihong Signed-off-by: Paul E. McKenney Tested-by: Yang Jihong Tested-by: Chen Zhongjin Reviewed-by: Frederic Weisbecker Signed-off-by: Boqun Feng --- init/init_task.c | 1 + 1 file changed, 1 insertion(+) (limited to 'init') diff --git a/init/init_task.c b/init/init_task.c index 7ecb458eb3da..4daee6d761c8 100644 --- a/init/init_task.c +++ b/init/init_task.c @@ -147,6 +147,7 @@ struct task_struct init_task __aligned(L1_CACHE_BYTES) = { .rcu_tasks_holdout = false, .rcu_tasks_holdout_list = LIST_HEAD_INIT(init_task.rcu_tasks_holdout_list), .rcu_tasks_idle_cpu = -1, + .rcu_tasks_exit_list = LIST_HEAD_INIT(init_task.rcu_tasks_exit_list), #endif #ifdef CONFIG_TASKS_TRACE_RCU .trc_reader_nesting = 0, -- cgit